Sima Ai or Sima Yi (277–304), courtesy name Shidu, formally Prince Li of Changsha, is a Jin Dynasty (265-420) imperial prince who briefly serves as regent for his brother Emperor Hui.

He is the fifth of the eight princes commonly associated with the War of the Eight Princes.

Of the eight princes, he alone receives praises from historians, for his attempt to reform government and his courtesy to his developmentally disabled brother the emperor.