diff --git a/src/router/index.ts b/src/router/index.ts
index bb6165d..9a57d05 100644
--- a/src/router/index.ts
+++ b/src/router/index.ts
@@ -12,6 +12,7 @@
 import { createRouter, createWebHistory } from "vue-router";
 import { useLoginStore } from "@/stores/login";
 import { getCookie, setCookie } from "@/utils/cookieUtil";
+import { encodeReturnTo } from "@/utils/returnToEncoding";
 import AuthContainer from "@/views/AuthContainer.vue";
 import MainContainer from "@/views/MainContainer.vue";
 import Login from "@/views/Login/LoginPage.vue";
@@ -182,7 +183,7 @@ function buildLoginRedirect(fullPath: string) {
   return {
     path: "/login",
     query: {
-      "return-to": btoa(fullPath),
+      "return-to": encodeReturnTo(fullPath),
     },
   };
 }
diff --git a/src/stores/login.ts b/src/stores/login.ts
index 59374de..4172941 100644
--- a/src/stores/login.ts
+++ b/src/stores/login.ts
@@ -13,6 +13,7 @@ import { defineStore } from "pinia";
 import axios from "axios";
 import apiClient from "@/api/client.js";
 import apiError from "@/module/apiError.js";
+import { decodeReturnTo } from "@/utils/returnToEncoding";
 import {
   deleteCookie,
   setCookie,
@@ -73,7 +74,7 @@ export const useLoginStore = defineStore("loginStore", {
         if (this.rememberedReturnToUrl !== "") {
           let decodedUrl = "";
           try {
-            decodedUrl = atob(this.rememberedReturnToUrl);
+            decodedUrl = decodeReturnTo(this.rememberedReturnToUrl);
           } catch {
             this.$router.push("/files");
             return;
diff --git a/src/utils/returnToEncoding.js b/src/utils/returnToEncoding.js
new file mode 100644
index 0000000..a5b15e6
--- /dev/null
+++ b/src/utils/returnToEncoding.js
@@ -0,0 +1,30 @@
+// The Lucia project.
+// Copyright 2026-2026 DSP, inc.  All rights reserved.
+// Authors:
+//   imacat.yang@dsp.im (imacat), 2026/03/08
+/** @module returnToEncoding UTF-8 safe base64 helpers for return-to paths. */
+
+/**
+ * Encodes a return-to path into UTF-8 safe base64.
+ * @param {string} returnToPath - The relative path to preserve.
+ * @returns {string} Base64-encoded UTF-8 string.
+ */
+export function encodeReturnTo(returnToPath) {
+  const bytes = new TextEncoder().encode(returnToPath);
+  let binary = "";
+  bytes.forEach((byte) => {
+    binary += String.fromCharCode(byte);
+  });
+  return btoa(binary);
+}
+
+/**
+ * Decodes a UTF-8 safe base64 return-to payload back to a path.
+ * @param {string} encodedReturnTo - Base64 payload from query parameter.
+ * @returns {string} Decoded path string.
+ */
+export function decodeReturnTo(encodedReturnTo) {
+  const binary = atob(encodedReturnTo);
+  const bytes = Uint8Array.from(binary, (char) => char.charCodeAt(0));
+  return new TextDecoder().decode(bytes);
+}
diff --git a/tests/router/routerGuard.test.js b/tests/router/routerGuard.test.js
index 8370802..600c654 100644
--- a/tests/router/routerGuard.test.js
+++ b/tests/router/routerGuard.test.js
@@ -4,6 +4,7 @@
 //   imacat.yang@dsp.im (imacat), 2026/03/06
 
 import { describe, it, expect, beforeEach } from "vitest";
+import { decodeReturnTo } from "@/utils/returnToEncoding";
 
 describe("router beforeEach guard logic", () => {
   beforeEach(() => {
@@ -70,7 +71,7 @@ describe("router beforeEach guard logic", () => {
       matched: [{ meta: { requiresAuth: true } }],
     });
     expect(result.path).toBe("/login");
-    expect(atob(result.query["return-to"])).toBe("/files");
+    expect(decodeReturnTo(result.query["return-to"])).toBe("/files");
   });
 
   it("allows requiresAuth route when refresh token can refresh session", () => {
@@ -100,7 +101,7 @@ describe("router beforeEach guard logic", () => {
       { refreshSucceeds: false },
     );
     expect(result.path).toBe("/login");
-    expect(atob(result.query["return-to"])).toBe(
+    expect(decodeReturnTo(result.query["return-to"])).toBe(
       "/discover/log/1/map?view=summary#node-2",
     );
   });
diff --git a/tests/unit/utils/returnToEncoding.test.js b/tests/unit/utils/returnToEncoding.test.js
new file mode 100644
index 0000000..0a85887
--- /dev/null
+++ b/tests/unit/utils/returnToEncoding.test.js
@@ -0,0 +1,21 @@
+// The Lucia project.
+// Copyright 2026-2026 DSP, inc.  All rights reserved.
+// Authors:
+//   imacat.yang@dsp.im (imacat), 2026/03/08
+
+import { describe, expect, it } from "vitest";
+import { encodeReturnTo, decodeReturnTo } from "@/utils/returnToEncoding";
+
+describe("returnToEncoding", () => {
+  it("round-trips ASCII paths", () => {
+    const original = "/discover/log/1/map?view=summary#node-2";
+    const encoded = encodeReturnTo(original);
+    expect(decodeReturnTo(encoded)).toBe(original);
+  });
+
+  it("round-trips Unicode paths without throwing", () => {
+    const original = "/files?keyword=流程圖#節點";
+    const encoded = encodeReturnTo(original);
+    expect(decodeReturnTo(encoded)).toBe(original);
+  });
+});