A piezoelectric actuator includes a square suspension plate, an outer frame, plural brackets and a square piezoelectric ceramic plate. The outer frame is arranged around the suspension plate. A second surface of the outer frame and a second surface of the suspension plate are coplanar with each other. The plural brackets are perpendicularly connected between the suspension plate and the outer frame for elastically supporting the suspension plate. Each bracket has a length in a range between 1.11 mm and 1.21 mm and a width in a range between 0.2 mm and 0.6 mm. A length of the piezoelectric ceramic plate is not larger than a length of the suspension plate. The piezoelectric ceramic plate is attached on a first surface of the suspension plate.