diff --git a/src/labelme2yolo/__about__.py b/src/labelme2yolo/__about__.py
index 485f66a..0822a15 100644
--- a/src/labelme2yolo/__about__.py
+++ b/src/labelme2yolo/__about__.py
@@ -4,4 +4,4 @@
 """
 about version
 """
-__version__ = "0.1.4"
+__version__ = "0.1.5"
diff --git a/src/labelme2yolo/l2y.py b/src/labelme2yolo/l2y.py
index 81dd6f3..92d1a1b 100644
--- a/src/labelme2yolo/l2y.py
+++ b/src/labelme2yolo/l2y.py
@@ -15,6 +15,7 @@ import shutil
 import uuid
 import logging
 
+from multiprocessing import Pool
 import PIL.ExifTags
 import PIL.Image
 import PIL.ImageOps
@@ -163,6 +164,20 @@ class Labelme2YOLO:
             self._label_id_map = {
                 label: label_id for label_id, label in enumerate(label_list)
             }
+        else:
+            # get label list from json files for parallel processing
+            json_files = glob.glob(
+                os.path.join(self._json_dir, "**", "*.json"), recursive=True
+            )
+            for json_file in json_files:
+                with open(json_file, encoding="utf-8") as file:
+                    json_data = json.load(file)
+                    for shape in json_data["shapes"]:
+                        if shape["label"] not in self._label_list:
+                            self._label_list.append(shape["label"])
+            self._label_id_map = {
+                label: label_id for label_id, label in enumerate(self._label_list)
+            }
 
     def _update_id_map(self, label: str):
         if label not in self._label_list:
@@ -230,8 +245,9 @@ class Labelme2YOLO:
         names = (train_json_names, val_json_names, test_json_names)
         for target_dir, json_names in zip(dirs, names):
             logger.info("Converting %s set ...", target_dir)
-            for json_name in tqdm.tqdm(json_names):
-                self.covert_json_to_text(target_dir, json_name)
+            with Pool(os.cpu_count() - 1) as pool:
+                for json_name in tqdm.tqdm(json_names):
+                    pool.apply(self.covert_json_to_text, (target_dir, json_name))
 
         self._save_dataset_yaml()