diff --git a/README.md b/README.md
index 29a1e1e..e450378 100644
--- a/README.md
+++ b/README.md
@@ -6,3 +6,4 @@ Convert pedestrian dataset to pascal voc or coco annotation structure. Compatibl
 - KAIST pedestrian dataset
 - SCUT FIR pedestrian dataset
 
+Please note that the pydatatool need vbb annotation file to convert. You need use [datatool](https://github.com/xzhewei/datatool) to convert the txt annotation file to vbb, then use this pydatatool.