diff --git a/fileserver/fileop.go b/fileserver/fileop.go
index 87a7ab5..46511f2 100644
--- a/fileserver/fileop.go
+++ b/fileserver/fileop.go
@@ -1472,6 +1472,11 @@ func postMultiFiles(rsp http.ResponseWriter, r *http.Request, repoID, parentDir,
 
 	canonPath := getCanonPath(parentDir)
 
+	if !replace && checkFilesWithSameName(repo, canonPath, fileNames) {
+		msg := "Too many files with same name.\n"
+		return &appError{nil, msg, http.StatusBadRequest}
+	}
+
 	for _, fileName := range fileNames {
 		if shouldIgnoreFile(fileName) {
 			msg := fmt.Sprintf("invalid fileName: %s.\n", fileName)
@@ -1558,6 +1563,26 @@ func postMultiFiles(rsp http.ResponseWriter, r *http.Request, repoID, parentDir,
 	return nil
 }
 
+func checkFilesWithSameName(repo *repomgr.Repo, canonPath string, fileNames []string) bool {
+	commit, err := commitmgr.Load(repo.ID, repo.HeadCommitID)
+	if err != nil {
+		return false
+	}
+	dir, err := fsmgr.GetSeafdirByPath(repo.StoreID, commit.RootID, canonPath)
+	if err != nil {
+		return false
+	}
+
+	for _, name := range fileNames {
+		uniqueName := genUniqueName(name, dir.Entries)
+		if uniqueName == "" {
+			return true
+		}
+	}
+
+	return false
+}
+
 func postFilesAndGenCommit(fileNames []string, repoID string, user, canonPath string, replace bool, ids []string, sizes []int64) (string, error) {
 	repo := repomgr.Get(repoID)
 	if repo == nil {
diff --git a/include/seafile-error.h b/include/seafile-error.h
index 8a3e26d..1564760 100644
--- a/include/seafile-error.h
+++ b/include/seafile-error.h
@@ -23,5 +23,6 @@
 #define POST_FILE_ERR_BLOCK_MISSING 518
 #define POST_FILE_ERR_QUOTA_FULL 519
 #define SEAF_ERR_CONCURRENT_UPLOAD 520
+#define SEAF_ERR_FILES_WITH_SAME_NAME 521
 
 #endif
diff --git a/server/repo-op.c b/server/repo-op.c
index d34718b..7c97bf3 100644
--- a/server/repo-op.c
+++ b/server/repo-op.c
@@ -1018,6 +1018,47 @@ format_json_ret (GList *name_list, GList *id_list, GList *size_list)
     return ret;
 }
 
+static gboolean
+check_files_with_same_name (SeafRepo *repo, const char *parent_dir, GList *filenames)
+{
+    char *canon_path = NULL;
+    SeafCommit *commit = NULL;
+    SeafDir *dir = NULL;
+    GError *error = NULL;
+    gboolean ret = FALSE;
+
+    GET_COMMIT_OR_FAIL(commit, repo->id, repo->version, repo->head->commit_id);
+
+    canon_path = get_canonical_path (parent_dir);
+
+    dir = seaf_fs_manager_get_seafdir_by_path (seaf->fs_mgr,
+                                               repo->store_id, repo->version,
+                                               commit->root_id,
+                                               canon_path, &error);
+    if (!dir) {
+        goto out;
+    }
+
+    GList *ptr;
+    for (ptr = filenames; ptr; ptr = ptr->next) {
+        char *name = ptr->data;
+        char *unique_name = NULL;
+        unique_name = generate_unique_filename (name, dir->entries);
+        if (!unique_name) {
+            ret = TRUE;
+            goto out;
+        }
+        g_free (unique_name);
+    }
+out:
+    g_clear_error (&error);
+    g_free (canon_path);
+    seaf_dir_free (dir);
+    seaf_commit_unref (commit);
+
+    return ret;
+}
+
 int
 seaf_repo_manager_post_multi_files (SeafRepoManager *mgr,
                                     const char *repo_id,
@@ -1053,6 +1094,13 @@ seaf_repo_manager_post_multi_files (SeafRepoManager *mgr,
         goto out;
     }
 
+    if (!replace_existed && check_files_with_same_name (repo, parent_dir, filenames))  {
+        seaf_debug ("[post files] Too many files with same name.\n");
+        g_set_error (error, SEAFILE_DOMAIN, SEAF_ERR_FILES_WITH_SAME_NAME, "Too many files with same name");
+        ret = -1;
+        goto out;
+    }
+
     /* Check inputs. */
     for (ptr = filenames; ptr; ptr = ptr->next) {
         filename = ptr->data;
diff --git a/server/upload-file.c b/server/upload-file.c
index d41346c..c860fb3 100755
--- a/server/upload-file.c
+++ b/server/upload-file.c
@@ -584,6 +584,9 @@ upload_api_cb(evhtp_request_t *req, void *arg)
         if (error) {
             if (error->code == POST_FILE_ERR_FILENAME) {
                 error_code = ERROR_FILENAME;
+            } else if (error->code == SEAF_ERR_FILES_WITH_SAME_NAME) {
+                error_code = -1;
+                send_error_reply (req, EVHTP_RES_BADREQ, "Too many files with same name.\n");
             }
             g_clear_error (&error);
         }
@@ -1196,6 +1199,9 @@ upload_ajax_cb(evhtp_request_t *req, void *arg)
         if (error) {
             if (error->code == POST_FILE_ERR_FILENAME) {
                 error_code = ERROR_FILENAME;
+            } else if (error->code == SEAF_ERR_FILES_WITH_SAME_NAME) {
+                error_code = -1;
+                send_error_reply (req, EVHTP_RES_BADREQ, "Too many files with same name.\n");
             }
             g_clear_error (&error);
         }