A simple and effective method was proposed for the fractionation of particles in suspensions. When suspensions were allowed to atomize ultrasonically, particles only having diameters in a limited range were contained in liquid particles formed by the atomization. Liquid droplets containing solid particles were collected to recover very fine solid particles. Aqueous suspensions of silica or bentonite particles were irradiated with a 2.4 MHz ultrasound, and fractions of fine solid particles were collected by recovering the mist used for transferring the liquid droplets. In addition, the separation performance was examined with a synthesized suspension, which was composed of silica particles having diameters of 100, 300, and 1000 nm. The recovered silica particles had diameters less than 300 nm and the cut-off diameter decreased with the addition of a surfactant. The results show high potential for the ultrasonic fractionation of particles using atomization.