Tian Chengsi (705 – March 4, 779), formally the Prince of Yanmen, was a Chinese military general, monarch, and politician. He served as a military general in the rebel state of Yan, who later submitted to and became a general of Tang Dynasty, from which Yan had rebelled. As was in the case of several other Yan generals who submitted to Tang but who had substantial army and territorial holdings, Tian was allowed to retain his command and territory, semi-independent from the Tang imperial government structure, and among these generals, he was particularly defiant of the Tang imperial government.