diff --git a/lib/thumbnail.lib.php b/lib/thumbnail.lib.php
index ebd9b4d79..2be693017 100644
--- a/lib/thumbnail.lib.php
+++ b/lib/thumbnail.lib.php
@@ -98,7 +98,7 @@ function thumbnail($filename, $source_path, $target_path, $thumb_width, $thumb_h
         @chmod($target_path, 0707);
     }
 
-    $thumb_file = "$target_path/thumb-{$thumb_filename}_{$thumb_width}x{$thumb_height}.png";
+    $thumb_file = "$target_path/thumb-{$thumb_filename}_{$thumb_width}x{$thumb_height}.jpg";
     $thumb_time = @filemtime($thumb_file);
     $source_file = "$source_path/$filename";
     $source_time = @filemtime($source_file);
@@ -112,7 +112,7 @@ function thumbnail($filename, $source_path, $target_path, $thumb_width, $thumb_h
     // 이미지 파일이 없거나 아님
     if (!$size[0]) {
         if (!$thumb_height) $thumb_height = $thumb_width;
-        $thumb_file = "$target_path/thumb-noimg_{$thumb_width}x{$thumb_height}.png";
+        $thumb_file = "$target_path/thumb-noimg_{$thumb_width}x{$thumb_height}.jpg";
         if (!file_exists($thumb_file)) {
             $target = imagecreate($thumb_width, $thumb_height);
             imagecolorallocate($target, 250, 250, 250);
@@ -162,7 +162,8 @@ function thumbnail($filename, $source_path, $target_path, $thumb_width, $thumb_h
         }
     }
 
-    imagepng($dst, $thumb_file, 0); // 0 (no compression) ~ 9
+    //imagepng($dst, $thumb_file, 9); // 0 (no compression) ~ 9
+    imagejpeg($dst, $thumb_file, 90);
     chmod($thumb_file, 0606); // 추후 삭제를 위하여 파일모드 변경
 
     return basename($thumb_file);