Ultrasonic atomization, in general, generates mist of liquid droplets with the diameter of micrometer order. Recently, our measurements with small-angle X-ray scattering (SAXS) at SPring-8 have revealed that the droplets of 1 nm dominate the whole population of atomized mist of ethanol. This article describes the details of SAXS measurements and discusess the mechanisms of the nano-sized droplet generation.