diff --git a/web/src/lib/auth-context.tsx b/web/src/lib/auth-context.tsx
index 21331c2..c7583f2 100644
--- a/web/src/lib/auth-context.tsx
+++ b/web/src/lib/auth-context.tsx
@@ -10,6 +10,7 @@ import {
   registerUser,
   getMe,
   setAuthToken,
+  setRefreshToken,
   setSyncEnabled,
   isAuthenticated as checkAuth,
   type AuthUser,
@@ -57,6 +58,7 @@ export function AuthProvider({ children }: { children: ReactNode }) {
     try {
       const result = await loginUser(email, password);
       setAuthToken(result.accessToken);
+      setRefreshToken(result.refreshToken);
       setSyncEnabled(true);
       setUser(result.user);
       return true;
@@ -72,6 +74,7 @@ export function AuthProvider({ children }: { children: ReactNode }) {
       try {
         const result = await registerUser(email, password, displayName);
         setAuthToken(result.accessToken);
+        setRefreshToken(result.refreshToken);
         setSyncEnabled(true);
         setUser(result.user);
         return true;
diff --git a/web/src/lib/platform-sync.ts b/web/src/lib/platform-sync.ts
index f64381a..0b9cd13 100644
--- a/web/src/lib/platform-sync.ts
+++ b/web/src/lib/platform-sync.ts
@@ -57,6 +57,7 @@ export interface OfflineQueueItem {
 
 const STORAGE_KEYS = {
   authToken: 'chronomind-auth-token',
+  refreshToken: 'chronomind-refresh-token',
   lastSync: 'chronomind-platform-last-sync',
   offlineQueue: 'chronomind-offline-queue',
   syncEnabled: 'chronomind-platform-sync-enabled',
@@ -76,6 +77,68 @@ function getAuthToken(): string | null {
   return localStorage.getItem(STORAGE_KEYS.authToken);
 }
 
+function getRefreshToken(): string | null {
+  if (typeof window === 'undefined') return null;
+  return localStorage.getItem(STORAGE_KEYS.refreshToken);
+}
+
+export function setRefreshToken(token: string | null): void {
+  if (typeof window === 'undefined') return;
+  if (token) {
+    localStorage.setItem(STORAGE_KEYS.refreshToken, token);
+  } else {
+    localStorage.removeItem(STORAGE_KEYS.refreshToken);
+  }
+}
+
+let _refreshPromise: Promise<boolean> | null = null;
+
+/**
+ * Attempt to refresh the access token using the stored refresh token.
+ * Returns true if refresh succeeded, false otherwise.
+ * Deduplicates concurrent refresh attempts.
+ */
+export async function refreshAccessToken(): Promise<boolean> {
+  if (_refreshPromise) return _refreshPromise;
+
+  _refreshPromise = (async () => {
+    const rt = getRefreshToken();
+    if (!rt) return false;
+
+    try {
+      const res = await fetch(`${getBaseUrl()}/auth/refresh`, {
+        method: 'POST',
+        headers: {
+          'Content-Type': 'application/json',
+          'x-product-id': PRODUCT_ID,
+          'x-request-id': crypto.randomUUID(),
+        },
+        body: JSON.stringify({ refreshToken: rt }),
+      });
+
+      if (!res.ok) {
+        // Refresh token is invalid/expired — clear both tokens
+        setAuthToken(null);
+        setRefreshToken(null);
+        return false;
+      }
+
+      const data = await res.json() as { accessToken: string; refreshToken: string };
+      setAuthToken(data.accessToken);
+      setRefreshToken(data.refreshToken);
+      return true;
+    } catch {
+      return false;
+    }
+  })();
+
+  try {
+    return await _refreshPromise;
+  } finally {
+    _refreshPromise = null;
+  }
+}
+
 async function apiRequest<T>(
   path: string,
   method: string,
@@ -100,6 +163,14 @@ async function apiRequest<T>(
     throw new SyncConflictError(data);
   }
 
+  // On 401, attempt a silent token refresh and retry once
+  if (res.status === 401 && !path.startsWith('/auth/')) {
+    const refreshed = await refreshAccessToken();
+    if (refreshed) {
+      return apiRequest<T>(path, method, body);
+    }
+  }
+
   if (!res.ok) {
     throw new Error(`Sync API error: ${res.status} ${res.statusText}`);
   }
@@ -122,6 +193,7 @@ export function setAuthToken(token: string | null): void {
     localStorage.setItem(STORAGE_KEYS.authToken, token);
   } else {
     localStorage.removeItem(STORAGE_KEYS.authToken);
+    localStorage.removeItem(STORAGE_KEYS.refreshToken);
   }
 }