diff --git a/src/api/auth.js b/src/api/auth.js
index fe9a37f..be8a0df 100644
--- a/src/api/auth.js
+++ b/src/api/auth.js
@@ -13,3 +13,8 @@ export async function register(username, password) {
     body: JSON.stringify({ username, password }),
   });
 }
+
+export async function logout() {
+  return apiFetch('/api/auth/logout', { method: 'POST' });
+}
+
diff --git a/src/api/client.js b/src/api/client.js
index 1ab9630..2b46a88 100644
--- a/src/api/client.js
+++ b/src/api/client.js
@@ -1,18 +1,84 @@
 const BASE = import.meta.env.VITE_API_BASE_URL || '';
 
+// 동시 401 발생 시 refresh를 한 번만 실행하기 위한 Promise 공유
+let refreshingPromise = null;
+
+async function tryRefresh() {
+  if (refreshingPromise) return refreshingPromise;
+
+  refreshingPromise = (async () => {
+    const rt = localStorage.getItem('refreshToken');
+    if (!rt) throw new Error('no_refresh_token');
+
+    const res = await fetch(BASE + '/api/auth/refresh', {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify({ refreshToken: rt }),
+    });
+
+    if (!res.ok) throw new Error('refresh_failed');
+
+    const data = await res.json();
+    localStorage.setItem('token', data.token);
+    localStorage.setItem('refreshToken', data.refreshToken);
+    return data.token;
+  })().finally(() => {
+    refreshingPromise = null;
+  });
+
+  return refreshingPromise;
+}
+
+async function doFetch(path, options, token) {
+  const headers = { 'Content-Type': 'application/json', ...options.headers };
+  if (token) headers['Authorization'] = `Bearer ${token}`;
+  return fetch(BASE + path, { ...options, headers });
+}
+
+async function parseError(res) {
+  let message = res.statusText;
+  try {
+    const body = await res.json();
+    if (body.error) message = body.error;
+  } catch {}
+  const err = new Error(message);
+  err.status = res.status;
+  return err;
+}
+
+// 204 No Content는 null 반환, 나머지는 JSON 파싱
+async function parseResponse(res) {
+  if (res.status === 204) return null;
+  return res.json();
+}
+
 export async function apiFetch(path, options = {}) {
   const token = localStorage.getItem('token');
-  const headers = { 'Content-Type': 'application/json', ...options.headers };
-  if (token) headers['Authorization'] = `Bearer ${token}`;
+  const res = await doFetch(path, options, token);
 
-  const res = await fetch(BASE + path, { ...options, headers });
   if (res.status === 401) {
-    window.dispatchEvent(new Event('auth:unauthorized'));
+    try {
+      const newToken = await tryRefresh();
+      // 새 토큰으로 원래 요청 재시도
+      const retryRes = await doFetch(path, options, newToken);
+      if (retryRes.status === 401) {
+        window.dispatchEvent(new Event('auth:unauthorized'));
+        throw await parseError(retryRes);
+      }
+      if (!retryRes.ok) throw await parseError(retryRes);
+      return parseResponse(retryRes);
+    } catch (e) {
+      // refresh 자체 실패 → 로그아웃
+      if (e.message === 'no_refresh_token' || e.message === 'refresh_failed') {
+        window.dispatchEvent(new Event('auth:unauthorized'));
+        const err = new Error('인증이 필요합니다');
+        err.status = 401;
+        throw err;
+      }
+      throw e;
+    }
   }
-  if (!res.ok) {
-    const err = new Error(res.statusText);
-    err.status = res.status;
-    throw err;
-  }
-  return res.json();
+
+  if (!res.ok) throw await parseError(res);
+  return parseResponse(res);
 }
diff --git a/src/components/AnnouncementBoard.jsx b/src/components/AnnouncementBoard.jsx
index d583327..beeab97 100644
--- a/src/components/AnnouncementBoard.jsx
+++ b/src/components/AnnouncementBoard.jsx
@@ -5,14 +5,18 @@ import './AnnouncementBoard.css';
 export default function AnnouncementBoard() {
   const [list, setList] = useState([]);
   const [expanded, setExpanded] = useState(null);
+  const [error, setError] = useState(false);
 
   useEffect(() => {
-    getAnnouncements().then(setList);
+    getAnnouncements()
+      .then(setList)
+      .catch(() => setError(true));
   }, []);
 
   return (
     <section className="announcement-board">
       <h2 className="announcement-heading">공지사항</h2>
+      {error && <p className="announcement-error">공지사항을 불러오지 못했습니다.</p>}
       <ul className="announcement-list">
         {list.map((item) => (
           <li key={item.id} className="announcement-item">
diff --git a/src/components/DownloadSection.jsx b/src/components/DownloadSection.jsx
index 6b0c6b6..592fdc2 100644
--- a/src/components/DownloadSection.jsx
+++ b/src/components/DownloadSection.jsx
@@ -22,7 +22,10 @@ export default function DownloadSection() {
       return;
     }
 
-    window.location.href = 'a301://launch?token=' + user.token;
+    // user.token은 로그인 시점 값으로 만료됐을 수 있으므로
+    // tryRefresh가 갱신한 최신 토큰을 localStorage에서 직접 읽음
+    const token = localStorage.getItem('token');
+    window.location.href = 'a301://launch?token=' + token;
   };
 
   const handleDownloadLauncher = () => {
diff --git a/src/components/admin/AnnouncementAdmin.jsx b/src/components/admin/AnnouncementAdmin.jsx
index e3c688c..98e35f6 100644
--- a/src/components/admin/AnnouncementAdmin.jsx
+++ b/src/components/admin/AnnouncementAdmin.jsx
@@ -8,14 +8,16 @@ export default function AnnouncementAdmin() {
   const [form, setForm] = useState({ title: '', content: '' });
   const [editingId, setEditingId] = useState(null);
   const [loading, setLoading] = useState(false);
+  const [error, setError] = useState('');
 
-  const load = () => getAnnouncements().then(setList);
+  const load = () => getAnnouncements().then(setList).catch(() => {});
   useEffect(() => { load(); }, []);
 
   const handleSubmit = async (e) => {
     e.preventDefault();
     if (!form.title || !form.content) return;
     setLoading(true);
+    setError('');
     try {
       if (editingId) {
         await apiFetch(`/api/announcements/${editingId}`, {
@@ -31,6 +33,8 @@ export default function AnnouncementAdmin() {
       setForm({ title: '', content: '' });
       setEditingId(null);
       load();
+    } catch (err) {
+      setError(err.message || '처리에 실패했습니다.');
     } finally {
       setLoading(false);
     }
@@ -39,17 +43,23 @@ export default function AnnouncementAdmin() {
   const handleEdit = (item) => {
     setEditingId(item.id);
     setForm({ title: item.title, content: item.content });
+    setError('');
   };
 
   const handleDelete = async (id) => {
     if (!confirm('삭제하시겠습니까?')) return;
-    await apiFetch(`/api/announcements/${id}`, { method: 'DELETE' });
-    load();
+    try {
+      await apiFetch(`/api/announcements/${id}`, { method: 'DELETE' });
+      load();
+    } catch (err) {
+      setError(err.message || '삭제에 실패했습니다.');
+    }
   };
 
   const handleCancel = () => {
     setEditingId(null);
     setForm({ title: '', content: '' });
+    setError('');
   };
 
   return (
@@ -70,6 +80,7 @@ export default function AnnouncementAdmin() {
           value={form.content}
           onChange={(e) => setForm({ ...form, content: e.target.value })}
         />
+        {error && <p className="admin-error">{error}</p>}
         <div className="admin-form-actions">
           <button className="btn-admin-primary" type="submit" disabled={loading}>
             {editingId ? '수정 완료' : '공지 등록'}
diff --git a/src/components/admin/DownloadAdmin.jsx b/src/components/admin/DownloadAdmin.jsx
index c3fd922..6c88371 100644
--- a/src/components/admin/DownloadAdmin.jsx
+++ b/src/components/admin/DownloadAdmin.jsx
@@ -31,6 +31,10 @@ function UploadForm({ title, hint, accept, endpoint, onSuccess }) {
 
     xhr.onload = () => {
       setUploading(false);
+      if (xhr.status === 401) {
+        window.dispatchEvent(new Event('auth:unauthorized'));
+        return;
+      }
       if (xhr.status >= 200 && xhr.status < 300) {
         onSuccess(JSON.parse(xhr.responseText));
         setFile(null);
@@ -50,6 +54,7 @@ function UploadForm({ title, hint, accept, endpoint, onSuccess }) {
 
     xhr.open('POST', `${BASE}${endpoint}?filename=${encodeURIComponent(file.name)}`);
     xhr.setRequestHeader('Authorization', `Bearer ${token}`);
+    xhr.setRequestHeader('Content-Type', 'application/octet-stream');
     setUploading(true);
     setError('');
     xhr.send(file);
diff --git a/src/components/admin/UserAdmin.jsx b/src/components/admin/UserAdmin.jsx
index a4643f6..0b6d9a5 100644
--- a/src/components/admin/UserAdmin.jsx
+++ b/src/components/admin/UserAdmin.jsx
@@ -5,27 +5,39 @@ import './AdminCommon.css';
 
 export default function UserAdmin() {
   const [users, setUsers] = useState([]);
+  const [error, setError] = useState('');
   const { user: me } = useAuth();
 
-  const load = () => getUsers().then(setUsers);
+  const load = () => getUsers().then(setUsers).catch(() => {});
   useEffect(() => { load(); }, []);
 
   const handleRoleToggle = async (u) => {
     const newRole = u.role === 'admin' ? 'user' : 'admin';
     if (!confirm(`${u.username}의 권한을 ${newRole}로 변경하시겠습니까?`)) return;
-    await updateUserRole(u.id, newRole);
-    load();
+    setError('');
+    try {
+      await updateUserRole(u.id, newRole);
+      load();
+    } catch (err) {
+      setError(err.message || '권한 변경에 실패했습니다.');
+    }
   };
 
   const handleDelete = async (u) => {
     if (!confirm(`${u.username} 계정을 삭제하시겠습니까?`)) return;
-    await deleteUser(u.id);
-    load();
+    setError('');
+    try {
+      await deleteUser(u.id);
+      load();
+    } catch (err) {
+      setError(err.message || '삭제에 실패했습니다.');
+    }
   };
 
   return (
     <div className="admin-section">
       <h2 className="admin-section-title">유저 관리</h2>
+      {error && <p className="admin-error">{error}</p>}
       <ul className="admin-list">
         {users.map((u) => (
           <li key={u.id} className="admin-list-item">
diff --git a/src/context/AuthContext.jsx b/src/context/AuthContext.jsx
index 58d91ce..93c0525 100644
--- a/src/context/AuthContext.jsx
+++ b/src/context/AuthContext.jsx
@@ -1,5 +1,5 @@
 import { useState, useCallback, useEffect } from 'react';
-import { login as apiLogin } from '../api/auth';
+import { login as apiLogin, logout as apiLogout } from '../api/auth';
 import { AuthContext } from './authContextValue';
 
 export function AuthProvider({ children }) {
@@ -13,22 +13,34 @@ export function AuthProvider({ children }) {
   const login = useCallback(async (username, password) => {
     const data = await apiLogin(username, password);
     localStorage.setItem('token', data.token);
+    localStorage.setItem('refreshToken', data.refreshToken);
     localStorage.setItem('username', data.username);
     localStorage.setItem('role', data.role);
     setUser({ token: data.token, username: data.username, role: data.role });
   }, []);
 
-  const logout = useCallback(() => {
+  // 로컬 세션만 정리 (토큰 만료·강제 로그아웃 시)
+  const clearSession = useCallback(() => {
     localStorage.removeItem('token');
+    localStorage.removeItem('refreshToken');
     localStorage.removeItem('username');
     localStorage.removeItem('role');
     setUser(null);
   }, []);
 
+  // 정상 로그아웃: 서버 세션(액세스 + 리프레시)도 삭제
+  const logout = useCallback(async () => {
+    try {
+      await apiLogout();
+    } catch {}
+    clearSession();
+  }, [clearSession]);
+
+  // 401 응답 시 서버 호출 없이 로컬 세션만 정리
   useEffect(() => {
-    window.addEventListener('auth:unauthorized', logout);
-    return () => window.removeEventListener('auth:unauthorized', logout);
-  }, [logout]);
+    window.addEventListener('auth:unauthorized', clearSession);
+    return () => window.removeEventListener('auth:unauthorized', clearSession);
+  }, [clearSession]);
 
   return (
     <AuthContext.Provider value={{ user, login, logout }}>
@@ -36,4 +48,3 @@ export function AuthProvider({ children }) {
     </AuthContext.Provider>
   );
 }
-