diff --git a/backend/emm-sale/src/main/java/com/emmsale/member/application/MemberActivityService.java b/backend/emm-sale/src/main/java/com/emmsale/member/application/MemberActivityService.java
index d5e1947e9..4aeb2e3b9 100644
--- a/backend/emm-sale/src/main/java/com/emmsale/member/application/MemberActivityService.java
+++ b/backend/emm-sale/src/main/java/com/emmsale/member/application/MemberActivityService.java
@@ -31,6 +31,9 @@ public void registerActivities(
       final Member member,
       final MemberActivityInitialRequest memberActivityInitialRequest
   ) {
+    if (member.isOnboarded()) {
+      throw new MemberException(MemberExceptionType.ALREADY_ONBOARDING);
+    }
     final List<Long> activityIds = memberActivityInitialRequest.getActivityIds();
     saveMemberActivities(member, activityIds);
 
@@ -62,11 +65,30 @@ public List<MemberActivityResponses> addActivity(
       final MemberActivityAddRequest memberActivityAddRequest
   ) {
     final List<Long> activityIds = memberActivityAddRequest.getActivityIds();
+    final List<MemberActivity> memberActivities = memberActivityRepository.findAllByMember(member);
+    if (isAlreadyExistActivity(memberActivities, activityIds) || hasDuplicateId(memberActivities,
+        activityIds)) {
+      throw new MemberException(MemberExceptionType.ALREADY_EXIST_ACTIVITY);
+    }
     saveMemberActivities(member, activityIds);
 
     return MemberActivityResponses.from(memberActivityRepository.findAllByMember(member));
   }
 
+  private boolean isAlreadyExistActivity(final List<MemberActivity> memberActivities,
+      final List<Long> activityIds) {
+    return memberActivities
+        .stream()
+        .anyMatch(memberActivity ->
+            activityIds.contains(memberActivity.getActivity().getId())
+        );
+  }
+
+  private boolean hasDuplicateId(final List<MemberActivity> memberActivities,
+      final List<Long> activityIds) {
+    return activityIds.stream().distinct().count() != memberActivities.size();
+  }
+
   public List<MemberActivityResponses> deleteActivity(
       final Member member,
       final MemberActivityDeleteRequest memberActivityDeleteRequest
diff --git a/backend/emm-sale/src/main/java/com/emmsale/member/exception/MemberExceptionType.java b/backend/emm-sale/src/main/java/com/emmsale/member/exception/MemberExceptionType.java
index 5c61feaa1..9a98bb11a 100644
--- a/backend/emm-sale/src/main/java/com/emmsale/member/exception/MemberExceptionType.java
+++ b/backend/emm-sale/src/main/java/com/emmsale/member/exception/MemberExceptionType.java
@@ -10,6 +10,11 @@ public enum MemberExceptionType implements BaseExceptionType {
       "해당 멤버는 존재하지 않습니다."
   ),
 
+  ALREADY_ONBOARDING(
+      HttpStatus.BAD_REQUEST,
+      "이미 온보딩을 완료한 사용자입니다."
+  ),
+
   INVALID_ACTIVITY_IDS(
       HttpStatus.BAD_REQUEST,
       "요청한 activity id들 중에 유효하지 않은 값이 존재합니다"
diff --git a/backend/emm-sale/src/test/java/com/emmsale/member/application/MemberActivityServiceTest.java b/backend/emm-sale/src/test/java/com/emmsale/member/application/MemberActivityServiceTest.java
index b9d445a5a..551ead007 100644
--- a/backend/emm-sale/src/test/java/com/emmsale/member/application/MemberActivityServiceTest.java
+++ b/backend/emm-sale/src/test/java/com/emmsale/member/application/MemberActivityServiceTest.java
@@ -108,7 +108,6 @@ void addActivity() throws Exception {
 
     //when
     final List<MemberActivityResponses> actual = memberActivityService.addActivity(member, request);
-
     //then
     assertThat(expected)
         .usingRecursiveComparison()
@@ -121,7 +120,7 @@ void addActivity() throws Exception {
   void test_addActivity_invalid_activity_ids_Exception() throws Exception {
     //given
     final Member savedMember = memberRepository.findById(1L).get();
-    final List<Long> activityIds = List.of(1L, 2L, 7L);
+    final List<Long> activityIds = List.of(4L, 5L, 7L);
     final MemberActivityAddRequest request = new MemberActivityAddRequest(activityIds);
 
     //when & then
@@ -138,10 +137,7 @@ void test_addActivity_ALREADY_EXIST_ACTIVITY_Exception_duplicate_try() throws Ex
     final List<Long> activityIds = List.of(1L, 2L, 7L);
     final MemberActivityAddRequest request = new MemberActivityAddRequest(activityIds);
 
-    // when
-    memberActivityService.addActivity(savedMember, request);
-
-    // then
+    // when, then
     assertThatThrownBy(() -> memberActivityService.addActivity(savedMember, request))
         .isInstanceOf(MemberException.class)
         .hasMessage(MemberExceptionType.ALREADY_EXIST_ACTIVITY.errorMessage());
@@ -152,7 +148,7 @@ void test_addActivity_ALREADY_EXIST_ACTIVITY_Exception_duplicate_try() throws Ex
   void test_addActivity_ALREADY_EXIST_ACTIVITY_Exception_duplicate_input() throws Exception {
     //given
     final Member savedMember = memberRepository.findById(1L).get();
-    final List<Long> activityIds = List.of(1L, 2L, 1L);
+    final List<Long> activityIds = List.of(4L, 4L, 5L);
     final MemberActivityAddRequest request = new MemberActivityAddRequest(activityIds);
 
     // when, then
diff --git a/backend/emm-sale/src/test/resources/data-test.sql b/backend/emm-sale/src/test/resources/data-test.sql
index 22365ae5a..4fa6785ae 100644
--- a/backend/emm-sale/src/test/resources/data-test.sql
+++ b/backend/emm-sale/src/test/resources/data-test.sql
@@ -28,7 +28,7 @@ insert into activity(id, type, name)
 values (6, 'JOB', 'Backend');
 
 insert into member(id, name, image_url, open_profile_url, github_id, created_at, updated_at)
-values (1, 'member1', 'https://imageurl.com', 'https://openprofileurl.com', 1, CURRENT_TIMESTAMP(),
+values (1, null, 'https://imageurl.com', 'https://openprofileurl.com', 1, CURRENT_TIMESTAMP(),
         CURRENT_TIMESTAMP());
 
 insert into member(id, name, image_url, open_profile_url, github_id, created_at, updated_at)