diff --git a/app/src/main/java/com/example/tampopo_client/viewmodels/ChatViewModel.java b/app/src/main/java/com/example/tampopo_client/viewmodels/ChatViewModel.java
index 80b1fce..3a5592e 100644
--- a/app/src/main/java/com/example/tampopo_client/viewmodels/ChatViewModel.java
+++ b/app/src/main/java/com/example/tampopo_client/viewmodels/ChatViewModel.java
@@ -9,6 +9,7 @@
 import com.example.tampopo_client.models.ChatMessage;
 import com.example.tampopo_client.models.Chatroom;
 import com.example.tampopo_client.models.Chatroom;
+import com.example.tampopo_client.resources.ActivitiesResource;
 import com.example.tampopo_client.resources.ChatroomResource;
 
 import java.io.IOException;
@@ -25,6 +26,7 @@
 
     private final Retrofit retrofit;
     private final ChatroomResource chatroomResource;
+    private final ActivitiesResource activitiesResource;
 
     // --- LiveData ---
     private final MutableLiveData<String> chatroomIdLiveData = new MutableLiveData<>();
@@ -58,6 +60,7 @@
                 .build();
 
         this.chatroomResource = retrofit.create(ChatroomResource.class);
+        this.activitiesResource = retrofit.create(ActivitiesResource.class);
     }
 
     public void setChatRoomId(String chatRoomId) {
@@ -76,6 +79,7 @@
                 .build();
 
         this.chatroomResource = retrofit.create(ChatroomResource.class);
+        this.activitiesResource = retrofit.create(ActivitiesResource.class);
     }
 
     @Override
@@ -123,6 +127,18 @@
 
 
     // ===============================
+    // ユーザーのアクティビティを更新
+    // ===============================
+    private void updateUserActivity(String userId, String token, String activityText) {
+        try {
+            Call<String> call = activitiesResource.addActivity(userId, token, activityText);
+            call.execute(); // 同期実行
+        } catch (IOException e) {
+            Log.e("ChatVM", "updateUserActivity error: " + e.getMessage());
+        }
+    }
+
+    // ===============================
     // 1. チャットルームに入る（かける側）
     // ===============================
     public String enterChatroom(String user0Id, String user1Id, String token) {
@@ -131,7 +147,13 @@
             Response<Chatroom> response = call.execute();
             if (response.isSuccessful() && response.body() != null) {
                 Log.d("OK","OK");
-                return response.body().getChatRoomId();
+                String chatRoomId = response.body().getChatRoomId();
+                
+                // 両方のユーザーのアクティビティを「通話中」に更新
+                updateUserActivity(user0Id, token, "通話中");
+                updateUserActivity(user1Id, token, "通話中");
+                
+                return chatRoomId;
             } else {
                 Log.d("Flase","Flase");
                 return null;
@@ -233,6 +255,15 @@
     }
 
     // ===============================
+    // 3.5. チャットルーム終了時のアクティビティクリア
+    // ===============================
+    public void clearChatActivities(String user0Id, String user1Id, String token) {
+        // 両方のユーザーのアクティビティを空文字列に更新
+        updateUserActivity(user0Id, token, "");
+        updateUserActivity(user1Id, token, "");
+    }
+
+    // ===============================
     // 4. チャットルーム削除
     // ===============================
     public void destroyChatroom(String chatroomId, String userId, String token) {