diff --git a/src/main/java/org/ntlab/tampoposerver/models/Activity.java b/src/main/java/org/ntlab/tampoposerver/models/Activity.java
index 207f3df..bd2781f 100644
--- a/src/main/java/org/ntlab/tampoposerver/models/Activity.java
+++ b/src/main/java/org/ntlab/tampoposerver/models/Activity.java
@@ -1,6 +1,10 @@
 package org.ntlab.tampoposerver.models;
 
+import com.fasterxml.jackson.annotation.JsonIdentityInfo;
+import com.fasterxml.jackson.annotation.JsonIgnore;
+
 public class Activity {
+    @JsonIgnore
     private String userId;
     private String activityId;
     private String text;