Li Jiancheng (589 – July 2, 626), formally Crown Prince Yin (iterally, "the hidden crown prince"), nickname Pishamen, is a crown prince of the Chinese dynasty Tang Dynasty.

He is the oldest son of the founding emperor Emperor Gaozu (Li Yuan) and therefore is designated crown prince after the founding of the dynasty in 618.

However, although he is fairly capable as a general, he is overshadowed by the contributions of his younger brother Li Shimin the Prince of Qin, and the brothers contend or power for years, with Li Jiancheng aided by another younger brother, Li Yuanji the Prince of Qi.

In 626, Li Shimin, fearing that Li Jiancheng and Li Yuanji were about to kill him, lays an ambush for them at Xuanwu Gate outside the palace and kills them.

Li Shimin then effectively forces Emperor Gaozu to yield the throne to him (as Emperor Taizong).