diff --git a/lib/mock/mock-agent.js b/lib/mock/mock-agent.js
index 3ab14949f35..61449e077ea 100644
--- a/lib/mock/mock-agent.js
+++ b/lib/mock/mock-agent.js
@@ -22,7 +22,7 @@ const {
 } = require('./mock-symbols')
 const MockClient = require('./mock-client')
 const MockPool = require('./mock-pool')
-const { matchValue, normalizeSearchParams, buildAndValidateMockOptions } = require('./mock-utils')
+const { matchValue, normalizeSearchParams, buildAndValidateMockOptions, normalizeOrigin } = require('./mock-utils')
 const { InvalidArgumentError, UndiciError } = require('../core/errors')
 const Dispatcher = require('../dispatcher/dispatcher')
 const PendingInterceptorsFormatter = require('./pending-interceptors-formatter')
@@ -56,9 +56,9 @@ class MockAgent extends Dispatcher {
   }
 
   get (origin) {
-    const originKey = this[kIgnoreTrailingSlash]
-      ? origin.replace(/\/$/, '')
-      : origin
+    // Normalize origin to handle URL objects and case-insensitive hostnames
+    const normalizedOrigin = normalizeOrigin(origin)
+    const originKey = this[kIgnoreTrailingSlash] ? normalizedOrigin.replace(/\/$/, '') : normalizedOrigin
 
     let dispatcher = this[kMockAgentGet](originKey)
 
@@ -70,6 +70,8 @@ class MockAgent extends Dispatcher {
   }
 
   dispatch (opts, handler) {
+    opts.origin = normalizeOrigin(opts.origin)
+
     // Call MockAgent.get to perform additional setup before dispatching as normal
     this.get(opts.origin)
 
diff --git a/lib/mock/mock-utils.js b/lib/mock/mock-utils.js
index 3b6d5b741bc..e1e3f040643 100644
--- a/lib/mock/mock-utils.js
+++ b/lib/mock/mock-utils.js
@@ -396,6 +396,18 @@ function checkNetConnect (netConnect, origin) {
   return false
 }
 
+function normalizeOrigin (origin) {
+  if (typeof origin !== 'string' && !(origin instanceof URL)) {
+    return origin
+  }
+
+  if (origin instanceof URL) {
+    return origin.origin
+  }
+
+  return origin.toLowerCase()
+}
+
 function buildAndValidateMockOptions (opts) {
   const { agent, ...mockOptions } = opts
 
@@ -430,5 +442,6 @@ module.exports = {
   buildAndValidateMockOptions,
   getHeaderByName,
   buildHeadersFromArray,
-  normalizeSearchParams
+  normalizeSearchParams,
+  normalizeOrigin
 }
diff --git a/test/mock-agent.js b/test/mock-agent.js
index f0b20e909e6..a0df6413a4e 100644
--- a/test/mock-agent.js
+++ b/test/mock-agent.js
@@ -2934,3 +2934,185 @@ test('MockAgent - should not accept non-standard search parameters when acceptNo
   const textResponse = await getResponse(body)
   t.assert.strictEqual(textResponse, '(non-intercepted) response from server')
 })
+
+// https://github.com/nodejs/undici/issues/4703
+describe('MockAgent - case-insensitive origin matching', () => {
+  test('should match origins with different hostname case', async (t) => {
+    t.plan(2)
+
+    const mockAgent = new MockAgent()
+    after(() => mockAgent.close())
+
+    const url1 = 'http://myEndpoint'
+    const url2 = 'http://myendpoint' // Different case
+
+    const mockPool = mockAgent.get(url1)
+    mockPool
+      .intercept({
+        path: '/test',
+        method: 'GET'
+      })
+      .reply(200, { success: true }, {
+        headers: { 'content-type': 'application/json' }
+      })
+
+    const { statusCode, body } = await mockAgent.request({
+      origin: url2, // Different case should still match
+      method: 'GET',
+      path: '/test'
+    })
+
+    t.assert.strictEqual(statusCode, 200)
+    const jsonResponse = JSON.parse(await getResponse(body))
+    t.assert.deepStrictEqual(jsonResponse, { success: true })
+  })
+
+  test('should match URL object origin with string origin', async (t) => {
+    t.plan(2)
+
+    const mockAgent = new MockAgent()
+    after(() => mockAgent.close())
+
+    const url = 'http://myEndpoint'
+
+    const mockPool = mockAgent.get(url)
+    mockPool
+      .intercept({
+        path: '/path',
+        method: 'GET'
+      })
+      .reply(200, { key: 'value' }, {
+        headers: { 'content-type': 'application/json' }
+      })
+
+    const { statusCode, body } = await mockAgent.request({
+      origin: new URL(url), // URL object should match string origin
+      method: 'GET',
+      path: '/path'
+    })
+
+    t.assert.strictEqual(statusCode, 200)
+    const jsonResponse = JSON.parse(await getResponse(body))
+    t.assert.deepStrictEqual(jsonResponse, { key: 'value' })
+  })
+
+  test('should match URL object with different hostname case', async (t) => {
+    t.plan(2)
+
+    const mockAgent = new MockAgent()
+    after(() => mockAgent.close())
+
+    const url1 = 'http://Example.com'
+    const url2 = new URL('http://example.com') // Different case
+
+    const mockPool = mockAgent.get(url1)
+    mockPool
+      .intercept({
+        path: '/test',
+        method: 'GET'
+      })
+      .reply(200, { success: true }, {
+        headers: { 'content-type': 'application/json' }
+      })
+
+    const { statusCode, body } = await mockAgent.request({
+      origin: url2, // URL object with different case should match
+      method: 'GET',
+      path: '/test'
+    })
+
+    t.assert.strictEqual(statusCode, 200)
+    const jsonResponse = JSON.parse(await getResponse(body))
+    t.assert.deepStrictEqual(jsonResponse, { success: true })
+  })
+
+  test('should handle mixed case scenarios correctly', async (t) => {
+    t.plan(2)
+
+    const mockAgent = new MockAgent()
+    after(() => mockAgent.close())
+
+    const url1 = 'http://MyEndpoint.com'
+    const url2 = 'http://myendpoint.com' // All lowercase
+
+    const mockPool = mockAgent.get(url1)
+    mockPool
+      .intercept({
+        path: '/api',
+        method: 'GET'
+      })
+      .reply(200, { data: 'test' }, {
+        headers: { 'content-type': 'application/json' }
+      })
+
+    const { statusCode, body } = await mockAgent.request({
+      origin: url2,
+      method: 'GET',
+      path: '/api'
+    })
+
+    t.assert.strictEqual(statusCode, 200)
+    const jsonResponse = JSON.parse(await getResponse(body))
+    t.assert.deepStrictEqual(jsonResponse, { data: 'test' })
+  })
+
+  test('should preserve port numbers when normalizing', async (t) => {
+    t.plan(2)
+
+    const mockAgent = new MockAgent()
+    after(() => mockAgent.close())
+
+    const url1 = 'http://Example.com:8080'
+    const url2 = 'http://example.com:8080' // Different case, same port
+
+    const mockPool = mockAgent.get(url1)
+    mockPool
+      .intercept({
+        path: '/test',
+        method: 'GET'
+      })
+      .reply(200, { port: 8080 }, {
+        headers: { 'content-type': 'application/json' }
+      })
+
+    const { statusCode, body } = await mockAgent.request({
+      origin: url2,
+      method: 'GET',
+      path: '/test'
+    })
+
+    t.assert.strictEqual(statusCode, 200)
+    const jsonResponse = JSON.parse(await getResponse(body))
+    t.assert.deepStrictEqual(jsonResponse, { port: 8080 })
+  })
+
+  test('should handle https origins with case differences', async (t) => {
+    t.plan(2)
+
+    const mockAgent = new MockAgent()
+    after(() => mockAgent.close())
+
+    const url1 = 'https://Api.Example.com'
+    const url2 = new URL('https://api.example.com') // Different case
+
+    const mockPool = mockAgent.get(url1)
+    mockPool
+      .intercept({
+        path: '/data',
+        method: 'GET'
+      })
+      .reply(200, { secure: true }, {
+        headers: { 'content-type': 'application/json' }
+      })
+
+    const { statusCode, body } = await mockAgent.request({
+      origin: url2,
+      method: 'GET',
+      path: '/data'
+    })
+
+    t.assert.strictEqual(statusCode, 200)
+    const jsonResponse = JSON.parse(await getResponse(body))
+    t.assert.deepStrictEqual(jsonResponse, { secure: true })
+  })
+})
diff --git a/test/mock-utils.js b/test/mock-utils.js
index 3b00242d8b7..873ac84014a 100644
--- a/test/mock-utils.js
+++ b/test/mock-utils.js
@@ -9,7 +9,8 @@ const {
   getStatusText,
   getHeaderByName,
   buildHeadersFromArray,
-  normalizeSearchParams
+  normalizeSearchParams,
+  normalizeOrigin
 } = require('../lib/mock/mock-utils')
 
 test('deleteMockDispatch - should do nothing if not able to find mock dispatch', (t) => {
@@ -268,3 +269,108 @@ describe('normalizeQueryParams', () => {
     t.assert.deepStrictEqual(normalizeSearchParams("a='1,2,3'").toString(), `a=${encodedSingleQuote}${encodeURIComponent('1,2,3')}${encodedSingleQuote}`)
   })
 })
+
+describe('normalizeOrigin', () => {
+  test('should normalize hostname to lowercase for string origins', (t) => {
+    t.plan(4)
+
+    t.assert.strictEqual(normalizeOrigin('http://Example.com'), 'http://example.com')
+    t.assert.strictEqual(normalizeOrigin('http://EXAMPLE.COM'), 'http://example.com')
+    t.assert.strictEqual(normalizeOrigin('https://Api.Example.com'), 'https://api.example.com')
+    t.assert.strictEqual(normalizeOrigin('http://MyEndpoint'), 'http://myendpoint')
+  })
+
+  test('should normalize hostname to lowercase for URL objects', (t) => {
+    t.plan(4)
+
+    t.assert.strictEqual(normalizeOrigin(new URL('http://Example.com')), 'http://example.com')
+    t.assert.strictEqual(normalizeOrigin(new URL('http://EXAMPLE.COM')), 'http://example.com')
+    t.assert.strictEqual(normalizeOrigin(new URL('https://Api.Example.com')), 'https://api.example.com')
+    t.assert.strictEqual(normalizeOrigin(new URL('http://MyEndpoint')), 'http://myendpoint')
+  })
+
+  test('should preserve port numbers', (t) => {
+    t.plan(3)
+
+    t.assert.strictEqual(normalizeOrigin('http://Example.com:8080'), 'http://example.com:8080')
+    t.assert.strictEqual(normalizeOrigin(new URL('http://Example.com:3000')), 'http://example.com:3000')
+    t.assert.strictEqual(normalizeOrigin(new URL('https://Test.com:8443')), 'https://test.com:8443')
+  })
+
+  test('should return RegExp matchers as-is', (t) => {
+    t.plan(1)
+
+    const regex = /http:\/\/example\.com/
+    t.assert.strictEqual(normalizeOrigin(regex), regex)
+  })
+
+  test('should return function matchers as-is', (t) => {
+    t.plan(1)
+
+    const fn = (origin) => origin === 'http://example.com'
+    t.assert.strictEqual(normalizeOrigin(fn), fn)
+  })
+
+  test('should return other non-string, non-URL types as-is', (t) => {
+    t.plan(4)
+
+    const obj = { origin: 'http://example.com' }
+    const num = 123
+    const bool = true
+    const nullValue = null
+
+    t.assert.strictEqual(normalizeOrigin(obj), obj)
+    t.assert.strictEqual(normalizeOrigin(num), num)
+    t.assert.strictEqual(normalizeOrigin(bool), bool)
+    t.assert.strictEqual(normalizeOrigin(nullValue), nullValue)
+  })
+
+  test('should handle invalid URLs gracefully', (t) => {
+    t.plan(2)
+
+    // Invalid URL strings should be returned as-is
+    t.assert.strictEqual(normalizeOrigin('not-a-url'), 'not-a-url')
+    t.assert.strictEqual(normalizeOrigin('://invalid'), '://invalid')
+  })
+
+  test('should handle IPv4 addresses', (t) => {
+    t.plan(2)
+
+    t.assert.strictEqual(normalizeOrigin('http://192.168.1.1'), 'http://192.168.1.1')
+    t.assert.strictEqual(normalizeOrigin('http://127.0.0.1:3000'), 'http://127.0.0.1:3000')
+  })
+
+  test('should handle IPv6 addresses', (t) => {
+    t.plan(2)
+
+    t.assert.strictEqual(normalizeOrigin('http://[::1]'), 'http://[::1]')
+    t.assert.strictEqual(normalizeOrigin('http://[2001:db8::1]:8080'), 'http://[2001:db8::1]:8080')
+  })
+
+  test('should handle localhost with different cases', (t) => {
+    t.plan(3)
+
+    t.assert.strictEqual(normalizeOrigin('http://LocalHost'), 'http://localhost')
+    t.assert.strictEqual(normalizeOrigin('http://LOCALHOST:3000'), 'http://localhost:3000')
+    t.assert.strictEqual(normalizeOrigin(new URL('http://LocalHost')), 'http://localhost')
+  })
+
+  test('should handle subdomains with mixed case', (t) => {
+    t.plan(3)
+
+    t.assert.strictEqual(normalizeOrigin('http://Api.Example.Com'), 'http://api.example.com')
+    t.assert.strictEqual(normalizeOrigin('https://WWW.Example.COM'), 'https://www.example.com')
+    t.assert.strictEqual(normalizeOrigin(new URL('http://Sub.Domain.Example.Com')), 'http://sub.domain.example.com')
+  })
+
+  test('should handle paths in URL objects (should only normalize origin part)', (t) => {
+    t.plan(2)
+
+    // URL objects with paths should still only return the origin
+    const url1 = new URL('http://Example.com/path/to/resource')
+    t.assert.strictEqual(normalizeOrigin(url1), 'http://example.com')
+
+    const url2 = new URL('https://Api.Example.com:8080/api/v1')
+    t.assert.strictEqual(normalizeOrigin(url2), 'https://api.example.com:8080')
+  })
+})