diff --git a/DevLog/App/Delegate/AppDelegate.swift b/DevLog/App/Delegate/AppDelegate.swift
index 2ee5924b..af8c6185 100644
--- a/DevLog/App/Delegate/AppDelegate.swift
+++ b/DevLog/App/Delegate/AppDelegate.swift
@@ -11,10 +11,15 @@ import FirebaseAuth
 import FirebaseFirestore
 import FirebaseMessaging
 import GoogleSignIn
+import Combine
 import UserNotifications
 
 class AppDelegate: UIResponder, UIApplicationDelegate, MessagingDelegate {
     private let logger = Logger(category: "AppDelegate")
+    private var store: Firestore { Firestore.firestore() }
+    private var authStateListenerHandle: AuthStateDidChangeListenerHandle?
+    private var cancellable: AnyCancellable?
+
     func application(
         _ app: UIApplication,
         open url: URL,
@@ -47,6 +52,7 @@ class AppDelegate: UIResponder, UIApplicationDelegate, MessagingDelegate {
 
         // Firebase Messaging 설정
         Messaging.messaging().delegate = self
+        observeAuthState()
         
         // 앱이 완전 종료되어도, 알림을 통해 앱이 시작된 경우 처리
         if let remoteNotification = launchOptions?[.remoteNotification] as? [AnyHashable: Any] {
@@ -73,6 +79,10 @@ class AppDelegate: UIResponder, UIApplicationDelegate, MessagingDelegate {
     ) {
         logger.error("Failed to register APNs token", error: error)
     }
+
+    func applicationDidBecomeActive(_ application: UIApplication) {
+        syncBadgeCount()
+    }
     
     // FCMToken 갱신
     func messaging(
@@ -83,8 +93,10 @@ class AppDelegate: UIResponder, UIApplicationDelegate, MessagingDelegate {
             NotificationCenter.default.post(name: .fcmToken, object: nil, userInfo: ["fcmToken": fcmToken])
         }
     }
+}
 
-    private func updateUserTimeZone() {
+private extension AppDelegate {
+    func updateUserTimeZone() {
         Task {
             do {
                 guard let uid = Auth.auth().currentUser?.uid else { return }
@@ -96,6 +108,122 @@ class AppDelegate: UIResponder, UIApplicationDelegate, MessagingDelegate {
             }
         }
     }
+
+    func observeAuthState() {
+        authStateListenerHandle = Auth.auth().addStateDidChangeListener { [weak self] _, user in
+            guard let self else { return }
+
+            self.cancellable?.cancel()
+
+            guard user != nil else {
+                self.updateBadgeCount(0)
+                return
+            }
+
+            self.startObservingBadgeCount()
+            self.syncBadgeCount()
+        }
+    }
+
+    func syncBadgeCount() {
+        Task { @MainActor [weak self] in
+            guard let self else { return }
+            guard Auth.auth().currentUser != nil else {
+                self.updateBadgeCount(0)
+                return
+            }
+
+            do {
+                let unreadNotificationCount = try await self.fetchUnreadNotificationCount()
+                self.updateBadgeCount(unreadNotificationCount)
+            } catch {
+                self.logger.error("Failed to fetch unread notification count", error: error)
+            }
+        }
+    }
+
+    private func startObservingBadgeCount() {
+        do {
+            cancellable = try observeUnreadNotificationCount()
+                .receive(on: DispatchQueue.main)
+                .sink(
+                    receiveCompletion: { [weak self] completion in
+                        guard let self else { return }
+
+                        if case .failure(let error) = completion {
+                            self.logger.error("Failed to observe unread notification count", error: error)
+                        }
+                    },
+                    receiveValue: { [weak self] count in
+                        self?.updateBadgeCount(count)
+                    }
+                )
+        } catch {
+            logger.error("Failed to start observing badge count", error: error)
+        }
+    }
+
+    private func fetchUnreadNotificationCount() async throws -> Int {
+        logger.info("Fetching unread notification count")
+
+        guard let uid = Auth.auth().currentUser?.uid else {
+            logger.error("User not authenticated")
+            throw AuthError.notAuthenticated
+        }
+
+        do {
+            let snapshot = try await store.collection("users/\(uid)/notifications")
+                .whereField("isRead", isEqualTo: false)
+                .getDocuments()
+
+            let unreadNotificationCount = snapshot.documents.count
+            logger.info("Unread notification count: \(unreadNotificationCount)")
+            return unreadNotificationCount
+        } catch {
+            logger.error("Failed to fetch unread notification count", error: error)
+            throw error
+        }
+    }
+
+    private func observeUnreadNotificationCount() throws -> AnyPublisher<Int, Error> {
+        logger.info("Observing unread notification count")
+
+        guard let uid = Auth.auth().currentUser?.uid else {
+            logger.error("User not authenticated")
+            throw AuthError.notAuthenticated
+        }
+
+        let subject = PassthroughSubject<Int, Error>()
+        let listener = store.collection("users/\(uid)/notifications")
+            .whereField("isRead", isEqualTo: false)
+            .addSnapshotListener { [weak self] snapshot, error in
+                guard let self else { return }
+                if let error {
+                    self.logger.error("Failed to observe unread notification count", error: error)
+                    subject.send(completion: .failure(error))
+                    return
+                }
+
+                guard let snapshot else { return }
+
+                let unreadNotificationCount = snapshot.documents.count
+                self.logger.info("Observed unread notification count: \(unreadNotificationCount)")
+                subject.send(unreadNotificationCount)
+            }
+
+        return subject
+            .handleEvents(receiveCancel: { listener.remove() })
+            .eraseToAnyPublisher()
+    }
+
+    @MainActor
+    private func updateBadgeCount(_ count: Int) {
+        UNUserNotificationCenter.current().setBadgeCount(count) { [weak self] error in
+            if let error {
+                self?.logger.error("Failed to update badge count", error: error)
+            }
+        }
+    }
 }
 
 extension AppDelegate: UNUserNotificationCenterDelegate {
diff --git a/Firebase/functions/src/fcm/notification.ts b/Firebase/functions/src/fcm/notification.ts
index 228dea09..16d3c9ac 100644
--- a/Firebase/functions/src/fcm/notification.ts
+++ b/Firebase/functions/src/fcm/notification.ts
@@ -97,9 +97,19 @@ export const sendPushNotification = onTaskDispatched({
             };
             await notificationDocRef.set(notificationData, { merge: true });
 
-            // 1. 사용자 FCM 토큰 가져오기
-            const tokenDoc = await admin.firestore().doc(`users/${userId}/userData/tokens`).get();
+            // 1. 사용자 FCM 토큰과 읽지 않은 알림 수 가져오기
+            const unreadCountPromise = admin.firestore()
+                .collection(`users/${userId}/notifications`)
+                .where("isRead", "==", false)
+                .count()
+                .get();
+            const tokenDocPromise = admin.firestore().doc(`users/${userId}/userData/tokens`).get();
+            const [tokenDoc, unreadCountSnapshot] = await Promise.all([
+                tokenDocPromise,
+                unreadCountPromise
+            ]);
             const fcmToken = tokenDoc.data()?.fcmToken;
+            const unreadNotificationCount = unreadCountSnapshot.data().count;
 
             if (!fcmToken) {
                 logger.warn(`사용자 ${userId}의 fcmToken이 없어 푸시 발송은 건너뜁니다. Firestore에는 기록했습니다.`);
@@ -113,7 +123,14 @@ export const sendPushNotification = onTaskDispatched({
                     todoId: todoId,
                     todoKind: todoKind
                 },
-                apns: { payload: { aps: { sound: "default" } } },
+                apns: {
+                    payload: {
+                        aps: {
+                            sound: "default",
+                            badge: unreadNotificationCount
+                        }
+                    }
+                },
                 token: fcmToken,
             };
             try {