diff --git a/app/client.ts b/app/client.ts
index 2a5ee69e..501841e5 100644
--- a/app/client.ts
+++ b/app/client.ts
@@ -22,6 +22,32 @@ const gtagFn: GtagFn = import.meta.env.PROD
       console.log('[gtag]', command, name, params)
     }
 
+interface Twq {
+  (...args: unknown[]): void
+  queue?: unknown[][]
+}
+
+const xPixelFn = import.meta.env.PROD
+  ? () => {
+      const w = window as Window & { twq?: Twq }
+      if (typeof w.twq === 'function') {
+        w.twq('event', 'tw-ov0j6-ov0j9', {})
+      } else {
+        // Initialize stub + queue if the base X pixel script (uwt.js) has not loaded yet.
+        // Mirrors the queuing behavior of the X base IIFE so early calls are not lost.
+        const queue: unknown[][] = []
+        const stub: Twq = (...args: unknown[]) => {
+          queue.push(args)
+        }
+        stub.queue = queue
+        w.twq = stub
+        stub('event', 'tw-ov0j6-ov0j9', {})
+      }
+    }
+  : () => {
+      console.log('[x-pixel]', 'event', 'tw-ov0j6-ov0j9', {})
+    }
+
 setupScrollDepthTracking({
   gtagFn,
   addScrollListener: (handler) => window.addEventListener('scroll', handler, { passive: true }),
@@ -83,4 +109,4 @@ setupMakamujoBannerTracking({
   maxDelayMs: 500,
 })
 
-setupDownloadAdPopup({ whenReady, gtagFn })
+setupDownloadAdPopup({ whenReady, gtagFn, xPixelFn })
diff --git a/app/components/DownloadAdDialog.test.ts b/app/components/DownloadAdDialog.test.ts
index f6cc2190..e266fa2d 100644
--- a/app/components/DownloadAdDialog.test.ts
+++ b/app/components/DownloadAdDialog.test.ts
@@ -97,6 +97,7 @@ function makeSetup(
     startDownload?: ReturnType<typeof vi.fn>
     hasDownloadUi?: () => boolean
     gtagFn?: ReturnType<typeof vi.fn>
+    xPixelFn?: ReturnType<typeof vi.fn>
     getPagePath?: () => string
     baseUrl?: string
   } = {},
@@ -119,6 +120,7 @@ function makeSetup(
     },
     startDownload: startDownloadFn,
     gtagFn: opts.gtagFn,
+    xPixelFn: opts.xPixelFn,
     getPagePath: opts.getPagePath,
     baseUrl: opts.baseUrl,
   })
@@ -277,6 +279,39 @@ describe('setupDownloadAdPopup', () => {
     expect(gtagFn).not.toHaveBeenCalled()
   })
 
+  it('fires X pixel conversion when xPixelFn is provided', () => {
+    const button = {
+      ...makeFakeButton('./test.pdf'),
+      textContent: 'ダウンロード',
+    }
+    const xPixelFn = vi.fn()
+    const { triggerClick } = makeSetup(button, { xPixelFn })
+
+    triggerClick()
+
+    expect(xPixelFn).toHaveBeenCalledTimes(1)
+  })
+
+  it('fires both GA and X pixel on download when both fns provided', () => {
+    const button = makeFakeButton()
+    const gtagFn = vi.fn()
+    const xPixelFn = vi.fn()
+    const { triggerClick } = makeSetup(button, { gtagFn, xPixelFn })
+
+    triggerClick()
+    expect(gtagFn).toHaveBeenCalled()
+    expect(xPixelFn).toHaveBeenCalled()
+  })
+
+  it('does not fire X pixel when xPixelFn is omitted', () => {
+    const button = makeFakeButton()
+    const xPixelFn = vi.fn()
+    const { triggerClick } = makeSetup(button)
+
+    triggerClick()
+    expect(xPixelFn).not.toHaveBeenCalled()
+  })
+
   it('opens cross-origin downloads in a new tab', () => {
     const button = makeFakeButton('https://example.com/file.zip', { sameOrigin: false, newTab: true })
     const { startDownloadFn, triggerClick } = makeSetup(button)
diff --git a/app/components/DownloadAdDialog.tsx b/app/components/DownloadAdDialog.tsx
index 0690065a..130ad8bd 100644
--- a/app/components/DownloadAdDialog.tsx
+++ b/app/components/DownloadAdDialog.tsx
@@ -36,6 +36,8 @@ export interface DownloadAdPopupOptions {
   baseUrl?: string
   /** Sends GA4 `file_download` events when a download button is clicked. */
   gtagFn?: GtagFn
+  /** Sends X Ads conversion event when a download button is clicked. */
+  xPixelFn?: () => void
   /** @internal Test override for the current page path sent as `link_id`. */
   getPagePath?: () => string
 }
@@ -128,6 +130,7 @@ export function setupDownloadAdPopup({
   hasDownloadUi = defaultHasDownloadUi,
   baseUrl,
   gtagFn,
+  xPixelFn,
   getPagePath = () => (typeof window !== 'undefined' ? window.location.pathname : ''),
 }: DownloadAdPopupOptions): void {
   whenReady(() => {
@@ -150,6 +153,9 @@ export function setupDownloadAdPopup({
         const linkText = button.textContent?.trim() ?? ''
         trackFileDownload(gtagFn, href, linkText, getPagePath())
       }
+      if (xPixelFn) {
+        xPixelFn()
+      }
       startDownloadFn(href, download, newTab)
     })
   })
diff --git a/app/components/RootLayout.tsx b/app/components/RootLayout.tsx
index 31f1d22f..7dd038ea 100644
--- a/app/components/RootLayout.tsx
+++ b/app/components/RootLayout.tsx
@@ -153,6 +153,19 @@ const gtagSnippets = {
 `,
 } as const
 
+const xPixelSnippets = {
+  body: html`\
+<!-- X conversion tracking base code -->
+<script>
+!function(e,t,n,s,u,a){e.twq||(s=e.twq=function(){s.exe?s.exe.apply(s,arguments):s.queue.push(arguments);
+},s.version='1.1',s.queue=[],u=t.createElement(n),u.async=!0,u.src='https://static.ads-twitter.com/uwt.js',
+a=t.getElementsByTagName(n)[0],a.parentNode.insertBefore(u,a))}(window,document,'script');
+twq('config','ov0j6');
+</script>
+<!-- End X conversion tracking base code -->
+`,
+} as const
+
 const OpenGraph = ({ url, image }: OpenGraphData) =>
   url || image ? (
     <>
@@ -203,6 +216,7 @@ const Layout = (props: PropsWithChildren<Meta>) => html`
 <body>
   ${props.children}
   ${import.meta.env.PROD ? gtagSnippets.body : html`<!-- -->\n`}\
+  ${import.meta.env.PROD && props.downloadAdPopup ? xPixelSnippets.body : html`<!-- -->\n`}\
 </body>
 </html>
 `