Xuzi 徐子 "Master Xu" was a Confucian treatise written by a certain Master Xu 徐氏 who lived in the state of Song 宋 during the Warring States period 戰國 (5th cent.-221 BCE). Some scholars say that he was a disciple of Meng Ke 孟軻, but this can be disproved by several textual evidences that demonstrate that he lived earlier than the great philosopher.
The imperial bibliography Yiwenzhi 藝文志 in the official dynastic history Hanshu 漢書 says that the book Xuzi was 42-chapters long. Of these, only one paragraph survives that is quoted in the books Weice 魏策 and Shiji 史記. This fragment was identified by Ma Guohan 馬國翰 (1794-1857) and is included in his series Yuhan shanfang jiyi shu 玉函山房輯佚書.