Xu Zhixun (徐知訓) (died 918) was the oldest biological son of Xu Wen, the regent of the Chinese Five Dynasties and Ten Kingdoms period state Wu. He served as the junior regent from 915 to his death in 918, with his father stationing himself at Jinling away from the capital Guangling (廣陵, in modern Yangzhou, Jiangsu). Xu Zhixun's arrogance alienated the Wu generals, and, in 918, after he angered the general Zhu Jin, Zhu assassinated him.
It is not known when Xu Zhixun was born, or who his mother was. He was the oldest known biological son of Xu Wen's, but was at one point referred to as Sanlang (三郎, "third-born son") by Song Qiqiu, implying that he might have had two older brothers who died in infancy and therefore were not counted in traditional counting of birth order. He had five younger biological brothers, Xu Zhixun (younger), Xu Zhihui (徐知誨), Xu Zhijian (徐知諫), Xu Zhizheng (徐知證), and Xu Zhi'e (徐知諤). It is not known whether Xu Wen's adoptive son Xu Zhigao was older or younger than he was, even though it was clear that Xu Zhigao was older than the younger Xu Zhixun.
It was said that Xu Zhixun tried to learn military strategies when he was young, but was not attentive to his studies. He favored combat games, both armed and unarmed. As, in his youth, Xu Wen had already become the regent of Wu, he, based on his father's status, was carrying out improper actions with impunity.
In 915, apparently in preparation for himself to be stationed outside Guangling, Xu Wen made Xu Zhixun, who was then a guard commander for the headquarters of Wu's prince Yang Longyan, the deputy commander of the Huainan Circuit (淮南, headquartered at Guangling) armed forces. Later in the year, Xu Wen left Guangling to take up a defense post at Run Prefecture (潤州, in modern Zhenjiang, Jiangsu), leaving Xu Zhixun at Guangling to govern affairs of the state, with he himself only ruling on important matters.