diff --git a/docs/source/index.rst b/docs/source/index.rst
index 53e5d15df5baaf307a3d0c24fce608af0d34a5e2..ea2599abe49e06c2b652488d073bda45a3a3b80e 100644
--- a/docs/source/index.rst
+++ b/docs/source/index.rst
@@ -23,7 +23,7 @@ Contents
    
 .. toctree::
    :maxdepth: 1
-   :caption: Speech-To-Text
+   :caption: Speech-to-Text
 
    asr/models_introduction
    asr/data_preparation
@@ -33,7 +33,7 @@ Contents
 
 .. toctree::
    :maxdepth: 1
-   :caption: Text-To-Speech
+   :caption: Text-to-Speech
 
    tts/basic_usage
    tts/advanced_usage