Sima Yun (simplified Chinese: 司马允; traditional Chinese: 司馬允; 272 - c.September 300), courtesy name Qindu (钦度),[6] posthumously known as Prince Zhongzhuang of Huainan, was an imperial prince of the Western Jin dynasty, and a son of Emperor Wu of Jin.
Sima Yun was born to Emperor Wu and his concubine Lady Li in 272; his full younger brother was Sima Yan (司马晏; 281 - 14 July 311[7]), Prince Xiao of Wu[8] and father to the future Emperor Min of Jin.
Sima Yun's half-brother Emperor Hui was developmentally disabled; his reign saw a series of regents who ruled on his behalf.
Sima Yun's activities during the regencies of Yang Jun, Yun's granduncle Sima Liang and Wei Guan (who were co-regents), and Emperor Hui's wife Empress Jia Nanfeng, were poorly documented.
The crown prince's fate lost Jia much support, and she was soon overthrown by Emperor Hui's grand-uncle Sima Lun in May.