Abstract: Disclosed is a nebulizer mounted to an ultrasonic humidifier. In the nebulizer, a heat sink holder can be directly connected to one side of a bottom plate in the humidifier, by using a flange provided at the upper end portion of the heat sink holder to which a heat sink for irradiating the heat generated in a PCB outward is mounted. Further, a vibrator assembled with the heat sink can be easily separated and replaced, because the heat sink is stacked on and assembled with the heat sink holder. Furthermore, the size of the ultrasonic humidifier is reduced, because a water level sensor is assembled and integrated with the upper surface of the heat sink. Furthermore, the durability of a vibrator as well as the heat sink is improved, because the heat sink is made of brass coated with a nickel plating layer.