Emperor Cheng of Jin (321 – 26 July 342), personal name Sima Yan, courtesy name Shigen, is an emperor of the Eastern Jin Dynasty (265-420).

He is the eldest son of Emperor Ming and becomes the crown prince on April 1, 325.

During his reign, the administration is largely dominated by a succession of regents—initially his uncle Yu Liang, then Wang Dao, then the joint administration of He Chong and another uncle Yu Bing.

He becomes emperor at age four, and soon after his accession to the throne, the disastrous rebellion of Su Jun weakens Jin forces for decades.