diff --git a/assets/css/src/amp-default.css b/assets/css/src/amp-default.css
index e8aae6e8712..558ffde7d84 100644
--- a/assets/css/src/amp-default.css
+++ b/assets/css/src/amp-default.css
@@ -61,3 +61,19 @@ body amp-audio:not([controls]) {
 .amp-wp-default-form-message[submit-success] > p:empty {
 	display: none;
 }
+
+amp-carousel .amp-wp-gallery-caption {
+	position: absolute;
+	bottom: 0;
+	left: 0;
+	right: 0;
+	text-align: center;
+	background-color: rgba(0, 0, 0, 0.5);
+	color: #fff;
+	padding: 1rem;
+}
+
+.wp-block-gallery[data-amp-carousel="true"] {
+	display: block;
+	flex-wrap: unset;
+}
diff --git a/includes/sanitizers/class-amp-gallery-block-sanitizer.php b/includes/sanitizers/class-amp-gallery-block-sanitizer.php
index 84a4c7f0f90..25779386fb6 100644
--- a/includes/sanitizers/class-amp-gallery-block-sanitizer.php
+++ b/includes/sanitizers/class-amp-gallery-block-sanitizer.php
@@ -73,23 +73,44 @@ class AMP_Gallery_Block_Sanitizer extends AMP_Base_Sanitizer {
 	 * @since 0.2
 	 */
 	public function sanitize() {
-		$nodes     = $this->dom->getElementsByTagName( self::$tag );
-		$num_nodes = $nodes->length;
-		if ( 0 === $num_nodes ) {
-			return;
+		$xpath       = new DOMXPath( $this->dom );
+		$class_query = 'contains( concat( " ", normalize-space( @class ), " " ), " wp-block-gallery " )';
+		$expr        = sprintf(
+			'//ul[ %s ]',
+			implode(
+				' or ',
+				[
+					sprintf( '( parent::figure[ %s ] )', $class_query ),
+					$class_query,
+				]
+			)
+		);
+		$query       = $xpath->query( $expr );
+
+		$nodes = [];
+		foreach ( $query as $node ) {
+			$nodes[] = $node;
 		}
 
-		for ( $i = $num_nodes - 1; $i >= 0; $i-- ) {
-			$node = $nodes->item( $i );
+		foreach ( $nodes as $node ) {
+			/**
+			 * Element
+			 *
+			 * @var DOMElement $node
+			 */
 
-			// We're looking for <ul> elements that have at least one child and the proper class.
-			if ( 0 === count( $node->childNodes ) || false === strpos( $node->getAttribute( 'class' ), self::$class ) ) {
-				continue;
-			}
+			// In WordPress 5.3, the Gallery block's <ul> is wrapped in a <figure class="wp-block-gallery">, so look for that node also.
+			$gallery_node = isset( $node->parentNode ) && AMP_DOM_Utils::has_class( $node->parentNode, self::$class ) ? $node->parentNode : $node;
+			$attributes   = AMP_DOM_Utils::get_node_attributes_as_assoc_array( $gallery_node );
 
-			$attributes      = AMP_DOM_Utils::get_node_attributes_as_assoc_array( $node );
 			$is_amp_lightbox = isset( $attributes['data-amp-lightbox'] ) && true === filter_var( $attributes['data-amp-lightbox'], FILTER_VALIDATE_BOOLEAN );
-			$is_amp_carousel = ! empty( $this->args['carousel_required'] ) || ( isset( $attributes['data-amp-carousel'] ) && true === filter_var( $attributes['data-amp-carousel'], FILTER_VALIDATE_BOOLEAN ) );
+			$is_amp_carousel = (
+				! empty( $this->args['carousel_required'] )
+				||
+				filter_var( $node->getAttribute( 'data-amp-carousel' ), FILTER_VALIDATE_BOOLEAN )
+				||
+				filter_var( $node->parentNode->getAttribute( 'data-amp-carousel' ), FILTER_VALIDATE_BOOLEAN )
+			);
 
 			// We are only looking for <ul> elements which have amp-carousel / amp-lightbox true.
 			if ( ! $is_amp_carousel && ! $is_amp_lightbox ) {
@@ -140,11 +161,46 @@ public function sanitize() {
 					'layout' => 'responsive',
 				]
 			);
+
 			foreach ( $images as $image ) {
-				$amp_carousel->appendChild( $image );
+				$slide = AMP_DOM_Utils::create_node(
+					$this->dom,
+					'div',
+					[ 'class' => 'slide' ]
+				);
+
+				// Ensure the image fills the entire <amp-carousel>, so the possible caption looks right.
+				if ( 'amp-img' === $image->tagName ) {
+					$image->setAttribute( 'layout', 'fill' );
+					$image->setAttribute( 'object-fit', 'cover' );
+				} elseif ( isset( $image->firstChild->tagName ) && 'amp-img' === $image->firstChild->tagName ) {
+					// If the <amp-img> is wrapped in an <a>.
+					$image->firstChild->setAttribute( 'layout', 'fill' );
+					$image->firstChild->setAttribute( 'object-fit', 'cover' );
+				}
+
+				$possible_caption_text = $this->possibly_get_caption_text( $image );
+				$slide->appendChild( $image );
+
+				// Wrap the caption in a <div> and <span>, and append it to the slide.
+				if ( $possible_caption_text ) {
+					$caption_wrapper = AMP_DOM_Utils::create_node(
+						$this->dom,
+						'div',
+						[ 'class' => 'amp-wp-gallery-caption' ]
+					);
+					$caption_span    = AMP_DOM_Utils::create_node( $this->dom, 'span', [] );
+					$text_node       = $this->dom->createTextNode( $possible_caption_text );
+
+					$caption_span->appendChild( $text_node );
+					$caption_wrapper->appendChild( $caption_span );
+					$slide->appendChild( $caption_wrapper );
+				}
+
+				$amp_carousel->appendChild( $slide );
 			}
 
-			$node->parentNode->replaceChild( $amp_carousel, $node );
+			$gallery_node->parentNode->replaceChild( $amp_carousel, $gallery_node );
 		}
 		$this->did_convert_elements = true;
 	}
@@ -219,4 +275,24 @@ protected function add_lightbox_attributes_to_image_nodes( $element ) {
 			}
 		}
 	}
+
+	/**
+	 * Gets the caption of an image, if it exists.
+	 *
+	 * @param DOMElement $element The element for which to search for a caption.
+	 * @return string|null The caption for the image, or null.
+	 */
+	public function possibly_get_caption_text( $element ) {
+		$caption_tag = 'figcaption';
+		if ( isset( $element->nextSibling->nodeName ) && $caption_tag === $element->nextSibling->nodeName ) {
+			return $element->nextSibling->textContent;
+		}
+
+		// If 'Link To' is selected, the image will be wrapped in an <a>, so search for the sibling of the <a>.
+		if ( isset( $element->parentNode->nextSibling->nodeName ) && $caption_tag === $element->parentNode->nextSibling->nodeName ) {
+			return $element->parentNode->nextSibling->textContent;
+		}
+
+		return null;
+	}
 }
diff --git a/tests/php/test-class-amp-gallery-block-sanitizer.php b/tests/php/test-class-amp-gallery-block-sanitizer.php
index b1542fbceec..b2b8cfabfa4 100644
--- a/tests/php/test-class-amp-gallery-block-sanitizer.php
+++ b/tests/php/test-class-amp-gallery-block-sanitizer.php
@@ -37,19 +37,50 @@ public function get_data() {
 				'<ul data-amp-carousel="true"><li class="blocks-gallery-item"><figure><a href="http://example.com"><amp-img src="http://example.com/img.png" width="600" height="400"></amp-img></a></figure></li></ul>',
 			],
 
-			'data_amp_with_carousel'              => [
+			'data_amp_with_carousel_and_link'     => [
 				'<ul class="wp-block-gallery" data-amp-carousel="true"><li class="blocks-gallery-item"><figure><a href="http://example.com"><amp-img src="http://example.com/img.png" width="600" height="400"></amp-img></a></figure></li></ul>',
-				'<amp-carousel width="600" height="400" type="slides" layout="responsive"><a href="http://example.com"><amp-img src="http://example.com/img.png" width="600" height="400"></amp-img></a></amp-carousel>',
+				'<amp-carousel width="600" height="400" type="slides" layout="responsive"><div class="slide"><a href="http://example.com"><amp-img src="http://example.com/img.png" width="600" height="400" layout="fill" object-fit="cover"></amp-img></a></div></amp-carousel>',
+			],
+
+			'data_amp_with_carousel_and_caption'  => [
+				'<ul class="wp-block-gallery" data-amp-carousel="true"><li class="blocks-gallery-item"><figure><amp-img src="http://example.com/img.png" width="600" height="400"></amp-img><figcaption>This is a caption</figcaption></figure></li></ul>',
+				'<amp-carousel width="600" height="400" type="slides" layout="responsive"><div class="slide"><amp-img src="http://example.com/img.png" width="600" height="400" layout="fill" object-fit="cover"></amp-img><div class="amp-wp-gallery-caption"><span>This is a caption</span></div></div></amp-carousel>',
+			],
+
+			// WordPress 5.3 changed the markup for the Gallery block, wrapping it in a <figure>.
+			'data_amp_with_carousel_caption_5_3'  => [
+				'<figure class="wp-block-gallery" data-amp-carousel="true"><ul><li class="blocks-gallery-item"><figure><amp-img src="http://example.com/img.png" width="600" height="400"></amp-img><figcaption>This is a caption</figcaption></figure></li></ul></figure>',
+				'<amp-carousel width="600" height="400" type="slides" layout="responsive"><div class="slide"><amp-img src="http://example.com/img.png" width="600" height="400" layout="fill" object-fit="cover"></amp-img><div class="amp-wp-gallery-caption"><span>This is a caption</span></div></div></amp-carousel>',
 			],
 
 			'data_amp_with_lightbox'              => [
+				'<ul class="wp-block-gallery" data-amp-lightbox="true"><li class="blocks-gallery-item"><figure><amp-img src="http://example.com/img.png" width="600" height="400"></amp-img></figure></li></ul>',
+				'<ul class="wp-block-gallery" data-amp-lightbox="true"><li class="blocks-gallery-item"><figure><amp-img src="http://example.com/img.png" width="600" height="400" data-amp-lightbox="" on="tap:amp-image-lightbox" role="button" tabindex="0"></amp-img></figure></li></ul><amp-image-lightbox id="amp-image-lightbox" layout="nodisplay" data-close-button-aria-label="Close"></amp-image-lightbox>',
+			],
+
+			'data_amp_with_lightbox_and_link'     => [
 				'<ul class="wp-block-gallery" data-amp-lightbox="true"><li class="blocks-gallery-item"><figure><a href="http://example.com"><amp-img src="http://example.com/img.png" width="600" height="400"></amp-img></a></figure></li></ul>',
 				'<ul class="wp-block-gallery" data-amp-lightbox="true"><li class="blocks-gallery-item"><figure><a href="http://example.com"><amp-img src="http://example.com/img.png" width="600" height="400" data-amp-lightbox="" on="tap:amp-image-lightbox" role="button" tabindex="0"></amp-img></a></figure></li></ul><amp-image-lightbox id="amp-image-lightbox" layout="nodisplay" data-close-button-aria-label="Close"></amp-image-lightbox>',
 			],
 
+			'data_amp_with_lightbox_5_3'          => [
+				'<figure class="wp-block-gallery" data-amp-lightbox="true"><ul><li class="blocks-gallery-item"><figure><amp-img src="http://example.com/img.png" width="600" height="400"></amp-img></figure></li></ul></figure>',
+				'<figure class="wp-block-gallery" data-amp-lightbox="true"><ul><li class="blocks-gallery-item"><figure><amp-img src="http://example.com/img.png" width="600" height="400" data-amp-lightbox="" on="tap:amp-image-lightbox" role="button" tabindex="0"></amp-img></figure></li></ul></figure><amp-image-lightbox id="amp-image-lightbox" layout="nodisplay" data-close-button-aria-label="Close"></amp-image-lightbox>',
+			],
+
+			'data_amp_with_lightbox_and_link_5_3' => [
+				'<figure class="wp-block-gallery" data-amp-lightbox="true"><ul><li class="blocks-gallery-item"><figure><a href="http://example.com"><amp-img src="http://example.com/img.png" width="600" height="400"></amp-img></a></figure></li></ul></figure>',
+				'<figure class="wp-block-gallery" data-amp-lightbox="true"><ul><li class="blocks-gallery-item"><figure><a href="http://example.com"><amp-img src="http://example.com/img.png" width="600" height="400" data-amp-lightbox="" on="tap:amp-image-lightbox" role="button" tabindex="0"></amp-img></a></figure></li></ul></figure><amp-image-lightbox id="amp-image-lightbox" layout="nodisplay" data-close-button-aria-label="Close"></amp-image-lightbox>',
+			],
+
 			'data_amp_with_lightbox_and_carousel' => [
 				'<ul class="wp-block-gallery" data-amp-lightbox="true" data-amp-carousel="true"><li class="blocks-gallery-item"><figure><a href="http://example.com"><amp-img src="http://example.com/img.png" width="1234" height="567"></amp-img></a></figure></li></ul>',
-				'<amp-carousel width="1234" height="567" type="slides" layout="responsive"><amp-img src="http://example.com/img.png" width="1234" height="567" data-amp-lightbox="" on="tap:amp-image-lightbox" role="button" tabindex="0"></amp-img></amp-carousel><amp-image-lightbox id="amp-image-lightbox" layout="nodisplay" data-close-button-aria-label="Close"></amp-image-lightbox>',
+				'<amp-carousel width="1234" height="567" type="slides" layout="responsive"><div class="slide"><amp-img src="http://example.com/img.png" width="1234" height="567" data-amp-lightbox="" on="tap:amp-image-lightbox" role="button" tabindex="0" layout="fill" object-fit="cover"></amp-img></div></amp-carousel><amp-image-lightbox id="amp-image-lightbox" layout="nodisplay" data-close-button-aria-label="Close"></amp-image-lightbox>',
+			],
+
+			'data_amp_with_lightbox_carousel_5_3' => [
+				'<figure class="wp-block-gallery" data-amp-lightbox="true" data-amp-carousel="true"><ul><li class="blocks-gallery-item"><figure><a href="http://example.com"><amp-img src="http://example.com/img.png" width="1234" height="567"></amp-img></a></figure></li></ul></figure>',
+				'<amp-carousel width="1234" height="567" type="slides" layout="responsive"><div class="slide"><amp-img src="http://example.com/img.png" width="1234" height="567" data-amp-lightbox="" on="tap:amp-image-lightbox" role="button" tabindex="0" layout="fill" object-fit="cover"></amp-img></div></amp-carousel><amp-image-lightbox id="amp-image-lightbox" layout="nodisplay" data-close-button-aria-label="Close"></amp-image-lightbox>',
 			],
 		];
 	}
@@ -91,14 +122,24 @@ public function get_reader_mode_data() {
 				'<ul data-amp-carousel="true"><li class="blocks-gallery-item"><figure><a href="http://example.com"><amp-img src="http://example.com/img.png" width="600" height="400"></amp-img></a></figure></li></ul>',
 			],
 
+			'data_amp_with_carousel_and_caption'  => [
+				'<ul class="wp-block-gallery" data-amp-carousel="true"><li class="blocks-gallery-item"><figure><a href="http://example.com"><amp-img src="http://example.com/img.png" width="600" height="400"></amp-img></a><figcaption>Here is a caption</figcaption></figure></li></ul>',
+				'<amp-carousel width="600" height="400" type="slides" layout="responsive"><div class="slide"><a href="http://example.com"><amp-img src="http://example.com/img.png" width="600" height="400" layout="fill" object-fit="cover"></amp-img></a><div class="amp-wp-gallery-caption"><span>Here is a caption</span></div></div></amp-carousel>',
+			],
+
 			'data_amp_with_lightbox'              => [
+				'<ul class="wp-block-gallery" data-amp-lightbox="true"><li class="blocks-gallery-item"><figure><amp-img src="http://example.com/img.png" width="600" height="400"></amp-img></figure></li></ul>',
+				'<amp-carousel width="600" height="400" type="slides" layout="responsive"><div class="slide"><amp-img src="http://example.com/img.png" width="600" height="400" data-amp-lightbox="" on="tap:amp-image-lightbox" role="button" tabindex="0" layout="fill" object-fit="cover"></amp-img></div></amp-carousel><amp-image-lightbox id="amp-image-lightbox" layout="nodisplay" data-close-button-aria-label="Close"></amp-image-lightbox>',
+			],
+
+			'data_amp_with_lightbox_and_link'     => [
 				'<ul class="wp-block-gallery" data-amp-lightbox="true"><li class="blocks-gallery-item"><figure><a href="http://example.com"><amp-img src="http://example.com/img.png" width="600" height="400"></amp-img></a></figure></li></ul>',
-				'<amp-carousel width="600" height="400" type="slides" layout="responsive"><amp-img src="http://example.com/img.png" width="600" height="400" data-amp-lightbox="" on="tap:amp-image-lightbox" role="button" tabindex="0"></amp-img></amp-carousel><amp-image-lightbox id="amp-image-lightbox" layout="nodisplay" data-close-button-aria-label="Close"></amp-image-lightbox>',
+				'<amp-carousel width="600" height="400" type="slides" layout="responsive"><div class="slide"><amp-img src="http://example.com/img.png" width="600" height="400" data-amp-lightbox="" on="tap:amp-image-lightbox" role="button" tabindex="0" layout="fill" object-fit="cover"></amp-img></div></amp-carousel><amp-image-lightbox id="amp-image-lightbox" layout="nodisplay" data-close-button-aria-label="Close"></amp-image-lightbox>',
 			],
 
-			'data_amp_with_lightbox_and_carousel' => [
+			'data_amp_lightbox_carousel_and_link' => [
 				'<ul class="wp-block-gallery" data-amp-lightbox="true" data-amp-carousel="true"><li class="blocks-gallery-item"><figure><a href="http://example.com"><amp-img src="http://example.com/img.png" width="600" height="400"></amp-img></a></figure></li></ul>',
-				'<amp-carousel width="600" height="400" type="slides" layout="responsive"><amp-img src="http://example.com/img.png" width="600" height="400" data-amp-lightbox="" on="tap:amp-image-lightbox" role="button" tabindex="0"></amp-img></amp-carousel><amp-image-lightbox id="amp-image-lightbox" layout="nodisplay" data-close-button-aria-label="Close"></amp-image-lightbox>',
+				'<amp-carousel width="600" height="400" type="slides" layout="responsive"><div class="slide"><amp-img src="http://example.com/img.png" width="600" height="400" data-amp-lightbox="" on="tap:amp-image-lightbox" role="button" tabindex="0" layout="fill" object-fit="cover"></amp-img></div></amp-carousel><amp-image-lightbox id="amp-image-lightbox" layout="nodisplay" data-close-button-aria-label="Close"></amp-image-lightbox>',
 			],
 		];
 	}
@@ -125,4 +166,60 @@ public function test_sanitizer_reader_mode( $source, $expected ) {
 		$content = preg_replace( '/(?<=>)\s+(?=<)/', '', $content );
 		$this->assertEquals( $expected, $content );
 	}
+
+	/**
+	 * Gets the data for test_possibly_get_caption_text().
+	 *
+	 * @return array[] The source to use, the expected return value, and the tag type to pass as an argument.
+	 */
+	public function get_caption_text_data() {
+		return [
+			'no_amp_img_or_anchor'       => [
+				'<div><img src="https://example.com/image.jpg"></div>',
+				null,
+				'img',
+			],
+			'amp_img_with_empty_caption' => [
+				'<amp-img src="https://example.com/image.jpg"></amp-img><figcaption></figcaption>',
+				null,
+				'amp-img',
+			],
+			'amp_img_with_caption'       => [
+				'<amp-img src="https://example.com/image.jpg"></amp-img><figcaption>This is a caption</figcaption>',
+				'This is a caption',
+				'amp-img',
+			],
+			'amp_img_wrapped_in_anchor_with_caption_in_div' => [
+				'<a href="https://example.com"><amp-img src="https://example.com/image.jpg"></amp-img></a><div>This is a caption</div>',
+				null,
+				'a',
+			],
+			'amp_img_wrapped_in_anchor_with_caption_in_figcaption' => [
+				'<a href="https://example.com"><amp-img src="https://example.com/image.jpg"></amp-img></a><figcaption>This is a caption</figcaption>',
+				'This is a caption',
+				'a',
+			],
+		];
+	}
+
+	/**
+	 * Test possibly_get_caption_text.
+	 *
+	 * @covers \AMP_Gallery_Block_Sanitizer::possibly_get_caption_text()
+	 *
+	 * @dataProvider get_caption_text_data
+	 * @param string      $source The markup source to test.
+	 * @param string|null $expected The expected return value of the tested method.
+	 * @param string      $element_name The name of the element to pass to the tested method.
+	 */
+	public function test_possibly_get_caption_text( $source, $expected, $element_name ) {
+		$dom       = AMP_DOM_Utils::get_dom_from_content( $source );
+		$element   = $dom->getElementsByTagName( $element_name )->item( 0 );
+		$sanitizer = new AMP_Gallery_Block_Sanitizer(
+			$dom,
+			[ 'content_max_width' => 600 ]
+		);
+
+		$this->assertEquals( $expected, $sanitizer->possibly_get_caption_text( $element ) );
+	}
 }