diff --git a/README.md b/README.md
index 8f08b4b..b3d9021 100644
--- a/README.md
+++ b/README.md
@@ -10,7 +10,11 @@ Usage:
 ./client SERVERNAME PORT FILENAME
 ```
 
-available macro:
+Server OPTION and arguments:
+- `-p port`   :set to port binding. couldn't set to 0
+- `-h`        :print help message.
+
+Available macro:
 - DEFAULT_SERVER_PORT : 9091
 - DEFAULT_MAX_PATH_SIZE : 256(must be less than 1000)
 - TIMEOUT : 5(second unit)