Il Sant'Alessio is an opera in three acts composed by Stefano Landi in 1631 with a libretto by Giulio Rospigliosi. Its first performance was probably in February 1632.

Stefano Landi was an Italian composer and teacher of the early Baroque Roman School. He was an influential early composer of opera, and wrote the earliest opera on a historical subject: Il Sant'Alessio (1632).