diff --git a/tomcat/src/main/java/nextstep/jwp/controller/ResisterController.java b/tomcat/src/main/java/nextstep/jwp/controller/ResisterController.java
index 11e62f82ab..0b1fb7d71b 100644
--- a/tomcat/src/main/java/nextstep/jwp/controller/ResisterController.java
+++ b/tomcat/src/main/java/nextstep/jwp/controller/ResisterController.java
@@ -26,6 +26,10 @@ protected void doPost(HttpRequest httpRequest, HttpResponse httpResponse) throws
         String email = httpRequest.getParam(EMAIL);
         String password = httpRequest.getParam(PASSWORD);
 
+        if (isDuplicateAccount(httpResponse, account)) {
+            return;
+        }
+
         User user = new User(account, password, email);
         InMemoryUserRepository.save(user);
         LOG.info("회원가입 성공한 회원 : {}", user);
@@ -37,6 +41,17 @@ protected void doPost(HttpRequest httpRequest, HttpResponse httpResponse) throws
         httpResponse.setLocation(INDEX_PAGE);
     }
 
+    private boolean isDuplicateAccount(HttpResponse httpResponse, String account) throws IOException {
+        if (InMemoryUserRepository.findByAccount(account).isPresent()) {
+            String content = FileReader.read(REGISTER_PAGE);
+            httpResponse.setHttpStatus(HttpStatus.BAD_REQUEST);
+            httpResponse.setContentType(ContentType.TEXT_HTML);
+            httpResponse.setBody(content);
+            return true;
+        }
+        return false;
+    }
+
     @Override
     protected void doGet(HttpRequest httpRequest, HttpResponse httpResponse) throws IOException {
         String content = FileReader.read(REGISTER_PAGE);
diff --git a/tomcat/src/main/java/org/apache/response/HttpStatus.java b/tomcat/src/main/java/org/apache/response/HttpStatus.java
index 364b2a9cb2..c9c443ba21 100644
--- a/tomcat/src/main/java/org/apache/response/HttpStatus.java
+++ b/tomcat/src/main/java/org/apache/response/HttpStatus.java
@@ -4,6 +4,7 @@ public enum HttpStatus {
 
     OK("200"),
     FOUND("302"),
+    BAD_REQUEST("400"),
     UNAUTHORIZED("401"),
     NOT_FOUND("404"),
     METHOD_NOT_ALLOWED("405");