diff --git a/src/main/java/life/mosu/mosuserver/application/oauth/OAuthUserPersistenceProcessor.java b/src/main/java/life/mosu/mosuserver/application/oauth/OAuthUserPersistenceProcessor.java
index 103814ca..7f21b7a0 100644
--- a/src/main/java/life/mosu/mosuserver/application/oauth/OAuthUserPersistenceProcessor.java
+++ b/src/main/java/life/mosu/mosuserver/application/oauth/OAuthUserPersistenceProcessor.java
@@ -16,12 +16,21 @@ public class OAuthUserPersistenceProcessor implements StepProcessor<OAuthUserInf
 
     private final UserJpaRepository userRepository;
 
+    /**
+     * this method is processing OAuthUserInfo to UserJpaEntity that is Get or Create.
+     *
+     * @param info
+     * @return
+     */
     @Override
     @Transactional
     public UserJpaEntity process(final OAuthUserInfo info) {
         return userRepository.findByPhoneNumber(
                         PhoneNumberUtil.formatPhoneNumber(info.phoneNumber()))
                 .map(existingUser -> {
+//                    if (existingUser.isMosuUser()) {
+//                        throw new IllegalArgumentException("이미 모수 회원입니다.");
+//                    }
                     existingUser.updateOAuthUser(
                             info.gender(),
                             info.name(),
diff --git a/src/main/java/life/mosu/mosuserver/application/oauth/OAuthUserService.java b/src/main/java/life/mosu/mosuserver/application/oauth/OAuthUserService.java
index d586ffdb..c3dc195d 100644
--- a/src/main/java/life/mosu/mosuserver/application/oauth/OAuthUserService.java
+++ b/src/main/java/life/mosu/mosuserver/application/oauth/OAuthUserService.java
@@ -5,6 +5,8 @@
 import java.util.Map;
 import life.mosu.mosuserver.domain.profile.repository.ProfileJpaRepository;
 import life.mosu.mosuserver.domain.user.entity.UserJpaEntity;
+import life.mosu.mosuserver.global.exception.CustomRuntimeException;
+import life.mosu.mosuserver.global.exception.ErrorCode;
 import lombok.RequiredArgsConstructor;
 import lombok.extern.slf4j.Slf4j;
 import org.springframework.core.ParameterizedTypeReference;
@@ -58,7 +60,10 @@ public OAuth2User loadUser(final OAuth2UserRequest userRequest)
                 oAuth2UserAttributes, agreedToMarketing);
 
         final UserJpaEntity oAuthUser = oAuthUserPersistenceProcessor.process(userInfo);
-        log.info("OAuthUser: {}", oAuthUser);
+        if (oAuthUser.isMosuUser()) {
+            log.info("모수 회원으로 가입된 사용자입니다: {}", oAuthUser.getLoginId());
+            throw new CustomRuntimeException(ErrorCode.ALREADY_MOSU_USER);
+        }
         Boolean isProfileRegistered = profileRepository.existsByUserId(oAuthUser.getId());
 
         return new OAuthUser(oAuthUser, oAuth2UserAttributes, userNameAttributeName,
diff --git a/src/main/java/life/mosu/mosuserver/global/exception/ErrorCode.java b/src/main/java/life/mosu/mosuserver/global/exception/ErrorCode.java
index e5f3f131..1e705d44 100644
--- a/src/main/java/life/mosu/mosuserver/global/exception/ErrorCode.java
+++ b/src/main/java/life/mosu/mosuserver/global/exception/ErrorCode.java
@@ -7,8 +7,8 @@
 @Getter
 @RequiredArgsConstructor
 public enum ErrorCode {
-
     // Principal 관련 에러
+    ALREADY_MOSU_USER(HttpStatus.BAD_REQUEST, "이미 모수 회원입니다."),
     PRINCIPAL_NOT_FOUND(HttpStatus.UNAUTHORIZED, "인증된 사용자를 찾을 수 없습니다."),
     LOGIN_BLOCKED(HttpStatus.UNAUTHORIZED, "로그인 시도가 차단되었습니다. 잠시 후 다시 시도해주세요."),
     TOO_MANY_REQUESTS(HttpStatus.TOO_MANY_REQUESTS, "요청이 너무 많습니다. 잠시 후 다시 시도해주세요."),