A piezoelectric speaker includes a cover with a receiving space and a vibrating speaker unit accommodated in the receiving space. The vibrating speaker unit includes a piezoelectric oscillator including an upper surface and an lower surface, a diaphragm disposed on the upper surface of the piezoelectric oscillator, and a vibrating member kept a distance from the lower surface of the piezoelectric oscillator. The piezoelectric oscillator defines a first amplitude capable of driving the diaphragm only and a second amplitude driving both the vibrating member to vibrating with a largest amplitude and the diaphragm to generate sound. The distance is larger than the first amplitude and smaller than the second amplitude.