diff --git a/.changelog/24183.txt b/.changelog/24183.txt
new file mode 100644
index 00000000000..a352ba78074
--- /dev/null
+++ b/.changelog/24183.txt
@@ -0,0 +1,7 @@
+```release-note:bug
+data-source/aws_eks_cluster: Return `created_at` as an [RFC3339](https://www.rfc-editor.org/rfc/rfc3339) formatted timestamp
+```
+
+```release-note:bug
+resource/aws_eks_cluster: Return `created_at` as an [RFC3339](https://www.rfc-editor.org/rfc/rfc3339) formatted timestamp
+```
diff --git a/internal/service/eks/cluster.go b/internal/service/eks/cluster.go
index 6321b6caa2a..36cbda1200a 100644
--- a/internal/service/eks/cluster.go
+++ b/internal/service/eks/cluster.go
@@ -463,7 +463,7 @@ func resourceClusterRead(ctx context.Context, d *schema.ResourceData, meta inter
 	if cluster.OutpostConfig != nil {
 		d.Set("cluster_id", cluster.Id)
 	}
-	d.Set(names.AttrCreatedAt, aws.ToTime(cluster.CreatedAt).String())
+	d.Set(names.AttrCreatedAt, cluster.CreatedAt.Format(time.RFC3339))
 	if err := d.Set("enabled_cluster_log_types", flattenLogging(cluster.Logging)); err != nil {
 		return sdkdiag.AppendErrorf(diags, "setting enabled_cluster_log_types: %s", err)
 	}
diff --git a/internal/service/eks/cluster_data_source.go b/internal/service/eks/cluster_data_source.go
index 0eb35a6247e..ee930388d6a 100644
--- a/internal/service/eks/cluster_data_source.go
+++ b/internal/service/eks/cluster_data_source.go
@@ -5,8 +5,8 @@ package eks
 
 import (
 	"context"
+	"time"
 
-	"github.com/aws/aws-sdk-go-v2/aws"
 	"github.com/hashicorp/terraform-plugin-sdk/v2/diag"
 	"github.com/hashicorp/terraform-plugin-sdk/v2/helper/schema"
 	"github.com/hashicorp/terraform-provider-aws/internal/conns"
@@ -243,7 +243,7 @@ func dataSourceClusterRead(ctx context.Context, d *schema.ResourceData, meta int
 	if cluster.OutpostConfig != nil {
 		d.Set("cluster_id", cluster.Id)
 	}
-	d.Set(names.AttrCreatedAt, aws.ToTime(cluster.CreatedAt).String())
+	d.Set(names.AttrCreatedAt, cluster.CreatedAt.Format(time.RFC3339))
 	if err := d.Set("enabled_cluster_log_types", flattenLogging(cluster.Logging)); err != nil {
 		return sdkdiag.AppendErrorf(diags, "setting enabled_cluster_log_types: %s", err)
 	}
diff --git a/internal/service/eks/cluster_test.go b/internal/service/eks/cluster_test.go
index a64056f7675..def9a2030ea 100644
--- a/internal/service/eks/cluster_test.go
+++ b/internal/service/eks/cluster_test.go
@@ -52,7 +52,7 @@ func TestAccEKSCluster_basic(t *testing.T) {
 					resource.TestCheckResourceAttr(resourceName, "certificate_authority.#", acctest.Ct1),
 					resource.TestCheckResourceAttrSet(resourceName, "certificate_authority.0.data"),
 					resource.TestCheckNoResourceAttr(resourceName, "cluster_id"),
-					resource.TestCheckResourceAttrSet(resourceName, names.AttrCreatedAt),
+					acctest.CheckResourceAttrRFC3339(resourceName, names.AttrCreatedAt),
 					resource.TestCheckResourceAttr(resourceName, "enabled_cluster_log_types.#", acctest.Ct0),
 					resource.TestCheckResourceAttr(resourceName, "encryption_config.#", acctest.Ct0),
 					resource.TestMatchResourceAttr(resourceName, names.AttrEndpoint, regexache.MustCompile(`^https://`)),