Xu You (died 204), courtesy name Ziyuan, was an adviser during the late Eastern Han dynasty of China.
The first mention of him was in 184, when he plotted with Wang Fen (王芬), the Inspector of Ji Province, and other officials to overthrow Emperor Ling (r. 168–189) and replace him with the Marquis of Hefei (合肥侯).
Eventually, the plot failed and Wang Fen committed suicide while Xu You fled.
Around 191, after the warlord Yuan Shao seized control of Ji Province from its governor Han Fu, he recruited Xu You to serve as an adviser under him.
Xu You, who was notorious for being greedy and corrupt, had allowed his family members to solicit bribes and commit crimes.
Shen Pei, another of Yuan Shao's subordinates who was in charge of coordinating the mobilisation of troops for the Guandu campaign, had Xu You's family members arrested.
Xu You pointed out the location of Yuan Shao's supply depot at Wuchao (烏巢) and urged Cao Cao to attack Wuchao and destroy Yuan Shao's supplies to force the enemy to retreat.