diff --git a/src/entities/session/model/useThoughtInbox.ts b/src/entities/session/model/useThoughtInbox.ts
index eeb3352..33bc084 100644
--- a/src/entities/session/model/useThoughtInbox.ts
+++ b/src/entities/session/model/useThoughtInbox.ts
@@ -1,94 +1,37 @@
 'use client';
 
 import { useCallback, useEffect, useMemo, useState } from 'react';
+import { copy } from '@/shared/i18n';
 import type { RecentThought } from './types';
+import { inboxApi } from '@/features/inbox/api/inboxApi';
 
-const THOUGHT_INBOX_STORAGE_KEY = 'viberoom:thought-inbox:v1';
 const MAX_THOUGHT_INBOX_ITEMS = 40;
 
-const readStoredThoughts = () => {
-  if (typeof window === 'undefined') {
-    return [];
-  }
-
-  const raw = window.localStorage.getItem(THOUGHT_INBOX_STORAGE_KEY);
-
-  if (!raw) {
-    return [];
-  }
-
-  try {
-    const parsed = JSON.parse(raw);
-
-    if (!Array.isArray(parsed)) {
-      return [];
-    }
-
-    return parsed.flatMap((thought): RecentThought[] => {
-      if (!thought || typeof thought !== 'object') {
-        return [];
-      }
-
-      const sceneName =
-        typeof thought.sceneName === 'string'
-          ? thought.sceneName
-          : typeof thought.roomName === 'string'
-            ? thought.roomName
-            : null;
-
-      if (
-        typeof thought.id !== 'string' ||
-        typeof thought.text !== 'string' ||
-        typeof thought.capturedAt !== 'string' ||
-        !sceneName ||
-        (typeof thought.isCompleted !== 'undefined' && typeof thought.isCompleted !== 'boolean')
-      ) {
-        return [];
-      }
-
-      return [
-        {
-          id: thought.id,
-          text: thought.text,
-          sceneName,
-          capturedAt: thought.capturedAt,
-          isCompleted: thought.isCompleted,
-        },
-      ];
-    });
-  } catch {
-    return [];
-  }
-};
-
-const persistThoughts = (thoughts: RecentThought[]) => {
-  if (typeof window === 'undefined') {
-    return;
-  }
-
-  window.localStorage.setItem(THOUGHT_INBOX_STORAGE_KEY, JSON.stringify(thoughts));
-};
-
 export const useThoughtInbox = () => {
-  const [thoughts, setThoughts] = useState<RecentThought[]>(() => readStoredThoughts());
+  const [thoughts, setThoughts] = useState<RecentThought[]>([]);
 
   useEffect(() => {
-    persistThoughts(thoughts);
-  }, [thoughts]);
-
-  useEffect(() => {
-    const handleStorage = (event: StorageEvent) => {
-      if (event.key !== THOUGHT_INBOX_STORAGE_KEY) {
-        return;
-      }
-
-      setThoughts(readStoredThoughts());
-    };
-
-    window.addEventListener('storage', handleStorage);
+    let mounted = true;
+    
+    inboxApi.getThoughts()
+      .then((data) => {
+        if (!mounted) return;
+        setThoughts(
+          data.map((d) => ({
+            id: d.id,
+            text: d.text,
+            sceneName: d.sceneName,
+            isCompleted: d.isCompleted,
+            capturedAt: copy.session.justNow,
+          }))
+        );
+      })
+      .catch((err) => {
+        console.error('Failed to load inbox thoughts:', err);
+      });
 
     return () => {
-      window.removeEventListener('storage', handleStorage);
+      mounted = false;
     };
   }, []);
 
@@ -99,20 +42,32 @@ export const useThoughtInbox = () => {
       return null;
     }
 
+    const tempId = `thought-temp-${Date.now()}-${Math.random().toString(16).slice(2, 8)}`;
+
     const thought: RecentThought = {
-      id: `thought-${Date.now()}-${Math.random().toString(16).slice(2, 8)}`,
+      id: tempId,
       text: trimmedText,
       sceneName,
-      capturedAt: '방금 전',
+      capturedAt: copy.session.justNow,
       isCompleted: false,
     };
 
     setThoughts((current) => {
       const next: RecentThought[] = [thought, ...current].slice(0, MAX_THOUGHT_INBOX_ITEMS);
-
       return next;
     });
 
+    inboxApi.addThought({ text: trimmedText, sceneName })
+      .then((res) => {
+        setThoughts((current) =>
+          current.map((t) => (t.id === tempId ? { ...t, id: res.id } : t))
+        );
+      })
+      .catch((err) => {
+        console.error('Failed to add thought:', err);
+        setThoughts((current) => current.filter((t) => t.id !== tempId));
+      });
+
     return thought;
   }, []);
 
@@ -131,6 +86,12 @@ export const useThoughtInbox = () => {
       return current.filter((thought) => thought.id !== thoughtId);
     });
 
+    if (removedThought && !thoughtId.startsWith('thought-temp-')) {
+      inboxApi.deleteThought(thoughtId).catch((err) => {
+        console.error('Failed to delete thought:', err);
+      });
+    }
+
     return removedThought;
   }, []);
 
@@ -142,6 +103,10 @@ export const useThoughtInbox = () => {
       return [];
     });
 
+    inboxApi.clearThoughts().catch((err) => {
+      console.error('Failed to clear thoughts:', err);
+    });
+
     return snapshot;
   }, []);
 
@@ -150,12 +115,44 @@ export const useThoughtInbox = () => {
       const withoutDuplicate = current.filter((currentThought) => currentThought.id !== thought.id);
       return [thought, ...withoutDuplicate].slice(0, MAX_THOUGHT_INBOX_ITEMS);
     });
+
+    inboxApi.addThought({ text: thought.text, sceneName: thought.sceneName })
+      .then((res) => {
+        setThoughts((current) =>
+          current.map((t) => (t.id === thought.id ? { ...t, id: res.id } : t))
+        );
+      })
+      .catch((err) => {
+        console.error('Failed to restore thought:', err);
+      });
   }, []);
 
   const restoreThoughts = useCallback((snapshot: RecentThought[]) => {
     setThoughts(() => {
       return snapshot.slice(0, MAX_THOUGHT_INBOX_ITEMS);
     });
+
+    // Fire and forget bulk restore as we don't have a bulk API
+    Promise.all(
+      snapshot.map((t) => inboxApi.addThought({ text: t.text, sceneName: t.sceneName }))
+    )
+      .then(() => {
+        return inboxApi.getThoughts();
+      })
+      .then((data) => {
+        setThoughts(
+          data.map((d) => ({
+            id: d.id,
+            text: d.text,
+            sceneName: d.sceneName,
+            isCompleted: d.isCompleted,
+            capturedAt: copy.session.justNow,
+          }))
+        );
+      })
+      .catch((err) => {
+        console.error('Failed to restore thoughts:', err);
+      });
   }, []);
 
   const setThoughtCompleted = useCallback((thoughtId: string, isCompleted: boolean) => {
@@ -178,6 +175,18 @@ export const useThoughtInbox = () => {
       return next;
     });
 
+    if (!thoughtId.startsWith('thought-temp-')) {
+      inboxApi.updateThoughtComplete(thoughtId, { isCompleted }).catch((err) => {
+        console.error('Failed to update thought completion:', err);
+        // Optionally revert state on failure
+        if (previousThought) {
+           setThoughts((current) => {
+             return current.map(t => t.id === thoughtId ? { ...t, isCompleted: !isCompleted } : t);
+           });
+        }
+      });
+    }
+
     return previousThought;
   }, []);
 
diff --git a/src/features/inbox/api/inboxApi.ts b/src/features/inbox/api/inboxApi.ts
new file mode 100644
index 0000000..60478e0
--- /dev/null
+++ b/src/features/inbox/api/inboxApi.ts
@@ -0,0 +1,57 @@
+import { apiClient } from '@/shared/lib/apiClient';
+
+export interface InboxThoughtResponse {
+  id: string;
+  text: string;
+  sceneName: string;
+  isCompleted: boolean;
+  capturedAt: string;
+}
+
+export interface CreateInboxThoughtRequest {
+  text: string;
+  sceneName: string;
+}
+
+export interface UpdateInboxThoughtRequest {
+  isCompleted: boolean;
+}
+
+export const inboxApi = {
+  getThoughts: async (): Promise<InboxThoughtResponse[]> => {
+    return apiClient<InboxThoughtResponse[]>('api/v1/inbox/thoughts', {
+      method: 'GET',
+    });
+  },
+
+  addThought: async (payload: CreateInboxThoughtRequest): Promise<InboxThoughtResponse> => {
+    return apiClient<InboxThoughtResponse>('api/v1/inbox/thoughts', {
+      method: 'POST',
+      body: JSON.stringify(payload),
+    });
+  },
+
+  updateThoughtComplete: async (
+    thoughtId: string,
+    payload: UpdateInboxThoughtRequest
+  ): Promise<InboxThoughtResponse> => {
+    return apiClient<InboxThoughtResponse>(`api/v1/inbox/thoughts/${thoughtId}/complete`, {
+      method: 'PUT',
+      body: JSON.stringify(payload),
+    });
+  },
+
+  deleteThought: async (thoughtId: string): Promise<void> => {
+    return apiClient<void>(`api/v1/inbox/thoughts/${thoughtId}`, {
+      method: 'DELETE',
+      expectNoContent: true,
+    });
+  },
+
+  clearThoughts: async (): Promise<void> => {
+    return apiClient<void>('api/v1/inbox/thoughts', {
+      method: 'DELETE',
+      expectNoContent: true,
+    });
+  },
+};