diff --git a/src/main/java/com/cmc/mercury/global/oauth/handler/OAuth2FailureHandler.java b/src/main/java/com/cmc/mercury/global/oauth/handler/OAuth2FailureHandler.java
index bfedffb..a6ca148 100644
--- a/src/main/java/com/cmc/mercury/global/oauth/handler/OAuth2FailureHandler.java
+++ b/src/main/java/com/cmc/mercury/global/oauth/handler/OAuth2FailureHandler.java
@@ -9,6 +9,8 @@
 import org.springframework.web.util.UriComponentsBuilder;
 
 import java.io.IOException;
+import java.net.URLEncoder;
+import java.nio.charset.StandardCharsets;
 
 @Component
 @Slf4j
@@ -19,8 +21,11 @@ public void onAuthenticationFailure(HttpServletRequest request, HttpServletRespo
                                         AuthenticationException exception) throws IOException {
 
         log.error("Social Login Failed: {}", exception.getMessage());
+        // 예외 메시지를 URI로 인코딩하여 전달
+        String errorMessage = URLEncoder.encode(exception.getMessage(), StandardCharsets.UTF_8);
 
         String targetUrl = UriComponentsBuilder.fromUriString("https://www.mercuryplanet.co.kr/login/fail")
+                .queryParam("error", errorMessage)
                 .build(true).toUriString();
 
         getRedirectStrategy().sendRedirect(request, response, targetUrl);
diff --git a/src/main/java/com/cmc/mercury/global/oauth/handler/OAuth2SuccessHandler.java b/src/main/java/com/cmc/mercury/global/oauth/handler/OAuth2SuccessHandler.java
index b4c50fd..a36c3ea 100644
--- a/src/main/java/com/cmc/mercury/global/oauth/handler/OAuth2SuccessHandler.java
+++ b/src/main/java/com/cmc/mercury/global/oauth/handler/OAuth2SuccessHandler.java
@@ -36,6 +36,8 @@ public void onAuthenticationSuccess(HttpServletRequest request, HttpServletRespo
                                         Authentication authentication) throws IOException {
         log.info("OAuth2 Login 성공!");
         OAuth2User oAuth2User = (OAuth2User) authentication.getPrincipal();
+        // 인증이 완료된 후 새로운 요청이 발생하면 request에 저장된 데이터(isNewUser). 는 사라짐
+        boolean isNewUser = (boolean) oAuth2User.getAttributes().getOrDefault("isNewUser", false);
 
         // oauthId로 사용자 조회
         User user = userRepository.findByOauthId(oAuth2User.getName())
@@ -62,6 +64,7 @@ public void onAuthenticationSuccess(HttpServletRequest request, HttpServletRespo
         // 리다이렉트 URL에 토큰 포함하여 이동
         String targetUrl = UriComponentsBuilder.fromUriString("https://www.mercuryplanet.co.kr/login/success")
                 .queryParam("access_token", accessToken)
+                .queryParam("isNewUser", isNewUser)
                 .build(true).toUriString();
 
         getRedirectStrategy().sendRedirect(request, response, targetUrl);
diff --git a/src/main/java/com/cmc/mercury/global/oauth/service/CustomOAuth2UserService.java b/src/main/java/com/cmc/mercury/global/oauth/service/CustomOAuth2UserService.java
index d7fe351..2058fb0 100644
--- a/src/main/java/com/cmc/mercury/global/oauth/service/CustomOAuth2UserService.java
+++ b/src/main/java/com/cmc/mercury/global/oauth/service/CustomOAuth2UserService.java
@@ -25,6 +25,7 @@
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.Map;
+import java.util.Optional;
 
 @Service
 @RequiredArgsConstructor
@@ -94,13 +95,19 @@ public OAuth2User loadUser(OAuth2UserRequest userRequest) throws OAuth2Authentic
             String oauthId = oAuth2UserInfo.getOAuthId();
             OAuthType oAuthType = oAuth2UserInfo.getOAuthType();
 
-            User user = userRepository.findByOauthTypeAndOauthId(oAuthType, oauthId)
-                    .orElseGet(() -> {
-                        log.info("새로운 사용자 생성 시도");
-                        return createUser(oAuth2UserInfo);
-                    });
+            Optional<User> existingUser = userRepository.findByOauthTypeAndOauthId(oAuthType, oauthId);
+            boolean isNewUser = existingUser.isEmpty(); // 존재하지 않으면 회원가입
+
+            User user = existingUser.orElseGet(() -> {
+                log.info("새로운 사용자 생성 시도");
+                return createUser(oAuth2UserInfo);
+            });
             log.info("사용자 조회/생성 완료: userId={}", user.getId());
 
+            // 회원가입 여부를 Security Context에 저장 (OAuth2User에 포함)
+            Map<String, Object> userAttributes = new HashMap<>(oAuth2User.getAttributes());
+            userAttributes.put("isNewUser", isNewUser);
+
             // 인증 객체 생성 (Security Context에 저장될 인증 정보)
             // 반환된 DefaultOAuth2User는 나중에 @AuthenticationPrincipal로 받아서 필요한 정보를 꺼내 쓸 수 있음
             return new DefaultOAuth2User(