When ultrasound is irradiated to liquid surface, small liquid droplets are generated from fountain jet. The purpose of this study is the estimation of the flow rate of droplet in ultrasonic atomization. The rectangular vessel was put on an electronic balance. An ultrasonic transducer at 2.4 MHz and 20 mm in diameter was installed at the center of the vessel bottom. In order to produce fountain jet without ultrasound, the liquid pump and nozzle was used. The mass change for ultrasound is larger than that for liquid pump. It is defined that the difference of mass changes between ultrasound and liquid pump is the flow rate of droplet. The flow rate of droplet in ultrasonic atomization increase with height of fountain jet and acoustic pressure.