diff --git a/README.md b/README.md
index 8d829c5f..1ee5900e 100644
--- a/README.md
+++ b/README.md
@@ -36,13 +36,20 @@ Actions to be taken for *ESP8266_RTOS_SDK v3.0* include the following items:
 
 ## Get toolchain
 
-You can get toolchain from arduio firstly.
+v5.2.0
 
 * [Windows](https://dl.espressif.com/dl/xtensa-lx106-elf-win32-1.22.0-92-g8facf4c-5.2.0.tar.gz)
 * [Mac](https://dl.espressif.com/dl/xtensa-lx106-elf-osx-1.22.0-92-g8facf4c-5.2.0.tar.gz)
 * [Linux(64)](https://dl.espressif.com/dl/xtensa-lx106-elf-linux64-1.22.0-92-g8facf4c-5.2.0.tar.gz)
 * [Linux(32)](https://dl.espressif.com/dl/xtensa-lx106-elf-linux32-1.22.0-92-g8facf4c-5.2.0.tar.gz)
 
+If you are still using old version SDK(< 3.0), please use toolchain v4.8.5, as following:
+
+* [Windows](https://dl.espressif.com/dl/xtensa-lx106-elf-win32-1.22.0-88-gde0bdc1-4.8.5.tar.gz)
+* [Mac](https://dl.espressif.com/dl/xtensa-lx106-elf-osx-1.22.0-88-gde0bdc1-4.8.5.tar.gz)
+* [Linux(64)](https://dl.espressif.com/dl/xtensa-lx106-elf-linux64-1.22.0-88-gde0bdc1-4.8.5.tar.gz)
+* [Linux(32)](https://dl.espressif.com/dl/xtensa-lx106-elf-linux32-1.22.0-88-gde0bdc1-4.8.5.tar.gz)
+
 ## Get ESP8266_RTOS_SDK
 
 Besides the toolchain (that contains programs to compile and build the application), you also need ESP8266 specific API / libraries. They are provided by Espressif in [ESP8266_RTOS_SDK](https://github.com/espressif/ESP8266_RTOS_SDK) repository. To get it, open terminal, navigate to the directory you want to put ESP8266_RTOS_SDK, and clone it using `git clone` command: