An ultrasonic wave nebulizer has a vibrator-heater assembly unit (4) mounted at bottom of a water container (1) for converting water to mist, and heating water to provide warm mist. The assembly unit (4) has a circular piezoelectric vibrator element (9), and a ring-shaped conductive plate (7) surrounding said vibrator element (9). A heater (11) is attached on the rear surface of the conductive plate (7) so that the heater (11) is out of water. The assembly unit (4) has also a circuit element (13) for energizing the vibrator element (9). Water is heated, preferably, at less than 70.degree. C.