A piezoelectric energy harvester is provided. The piezoelectric energy harvester includes a housing, a metal plate, a first piezoelectric material, an auto-returning device, a movable supporter, a first magnet and a second magnet. The housing includes a bottom plate, a top plate, a first side wall and a second side wall. A first terminal of the metal plate is fixed on the first side wall and a second terminal of the metal plate extends toward the second side wall. The first piezoelectric material is disposed on the metal plate to be deformed when the metal plate is deformed. When the movable supporter is moved, the movable supporter can push the second terminal of the metal plate to deform the metal plate. The first magnet and the second magnet are respectively disposed on the bottom plate and the top plate to attract the second terminal of the metal plate.