diff --git a/apps/mobile/src/lib/mobile-note-image-export.test.ts b/apps/mobile/src/lib/mobile-note-image-export.test.ts
index b8e3f62b..d63f6b1a 100644
--- a/apps/mobile/src/lib/mobile-note-image-export.test.ts
+++ b/apps/mobile/src/lib/mobile-note-image-export.test.ts
@@ -1,5 +1,25 @@
 import { describe, expect, test } from "bun:test";
-import { planMobileNoteImageRender } from "./mobile-note-image-export";
+import { PathUtilities } from "../../node_modules/expo-file-system/src/pathUtilities";
+import { buildImageExportBasename } from "@edgeever/shared/note-image-card";
+import { encodeMobileNoteImageFileUri, planMobileNoteImageRender } from "./mobile-note-image-export";
+
+describe("mobile note image file URI", () => {
+  test.each(["png", "jpg"])("preserves bracketed titles for %s exports through Expo path joining", (extension) => {
+    const filename = `${buildImageExportBasename("[Serv00.com] Account activation tuuki", "Untitled")}.${extension}`;
+    const uri = encodeMobileNoteImageFileUri(PathUtilities.join("file:///cache/exports/request-1/", filename));
+    expect(uri).toBe(`file:///cache/exports/request-1/%5BServ00.com%5D%20Account%20activation%20tuuki.${extension}`);
+    // File's constructor joins the URI once more before handing it to Android.
+    expect(PathUtilities.join(uri)).toBe(uri);
+    expect(decodeURIComponent(new URL(uri).pathname.split("/").at(-1)!)).toBe(filename);
+  });
+
+  test.each(["中文 [标题] 100% #1.png", "literal %5Bname%5D.png", "普通笔记.jpg"])("preserves the filename %s without double encoding", (filename) => {
+    const uri = encodeMobileNoteImageFileUri(PathUtilities.join("file:///cache/exports/", filename));
+    expect(uri).not.toMatch(/[\[\]]/);
+    expect(decodeURIComponent(new URL(uri).pathname.split("/").at(-1)!)).toBe(filename);
+    expect(encodeMobileNoteImageFileUri(uri)).toBe(uri);
+  });
+});
 
 describe("planMobileNoteImageRender", () => {
   test("keeps a short card at full quality", () => {
diff --git a/apps/mobile/src/lib/mobile-note-image-export.ts b/apps/mobile/src/lib/mobile-note-image-export.ts
index c159167a..c3a01abf 100644
--- a/apps/mobile/src/lib/mobile-note-image-export.ts
+++ b/apps/mobile/src/lib/mobile-note-image-export.ts
@@ -1 +1,7 @@
 export { planNativeNoteImageRender as planMobileNoteImageRender } from "@edgeever/shared/note-image-card";
+
+// Expo's path joiner escapes spaces and percent signs, but leaves brackets raw.
+// Android's java.net.URI rejects those in a path. Escape only brackets here so
+// existing percent escapes stay intact and the actual filename is preserved.
+export const encodeMobileNoteImageFileUri = (uri: string): string =>
+  uri.replace(/\[/g, "%5B").replace(/\]/g, "%5D");
diff --git a/apps/mobile/src/screens/WorkspaceMemoDetail.tsx b/apps/mobile/src/screens/WorkspaceMemoDetail.tsx
index df45ffd6..fb7feefd 100644
--- a/apps/mobile/src/screens/WorkspaceMemoDetail.tsx
+++ b/apps/mobile/src/screens/WorkspaceMemoDetail.tsx
@@ -26,6 +26,7 @@ import { getMobileNoteImageFontLabel } from "../lib/note-image-font-options";
 import { MobileResourceActions } from "../components/MobileResourceActions";
 import { ZoomableImagePreview } from "../components/ZoomableImagePreview";
 import type { ImageSize } from "../lib/mobile-image-zoom";
+import { encodeMobileNoteImageFileUri } from "../lib/mobile-note-image-export";
 import { SAFE_DOM_WEBVIEW_PROPS } from "../lib/mobile-dom";
 import { getNextMobileNoteSearchIndex } from "../lib/mobile-note-search";
 import { hasMobilePoster, hasMobileInfographic, hasMobileStructuredTable, hasMobileVisualDiagram, resolveMobileMemoViewerContent } from "../lib/mobile-diagram";
@@ -972,7 +973,7 @@ export const MemoDetailModal = ({
       // earlier export when different notes share the same download filename.
       const directory = new Directory(Paths.cache, "edgeever-note-exports", event.requestId);
       if (!directory.exists) directory.create({ idempotent: true, intermediates: true });
-      const file = new File(directory, event.filename);
+      const file = new File(encodeMobileNoteImageFileUri(Paths.join(directory, event.filename)));
       if (file.exists) file.delete();
       file.create({ overwrite: true, intermediates: true });
       file.write(decodeBase64Chunks(imageExportChunksRef.current));