A theory of ultrasonic atomization of liquid films is presented. It is assumed that exponential growth of surface disturbances ultimately results in the formation of liquid drops, the diameters of which are proportional to the wavelength of the most rapidly growing initial disturbance. The hydrodynamic stability equations of the liquid film are examined, and the most rapidly growing initial disturbances are determined by numerical solution in the unstable region. A resultant correlation between drop size, transducer frequency, transducer amplitude, and liquid‐film thickness is obtained. Results are compared to previous theoretical and experimental conclusions.