High frequency ultrasound was applied to an emulsion to enhance the separation of emulsions into oil and water. The emulsion sample was prepared with mixing a mixture of dodecane, water and Span 80 as a surfactant. Volumetric ratio of water to oil was 1.5 and water in oil type emulsion was formed. Ultrasound of 2.4MHz was irradiated from the bottom of a cylindrical reservoir to the emulsion of 100cm^3. Emulsion separation was successfully enhanced by the ultrasonic irradiation. A layer of dodecane, continuous phase, appeared after a pretreatment for the turbidity analysis. A part of the layer was taken out and the absorbance at 800nm was measured to determine the degree of separation. Under applied power of 11W, time for the separation is about one fourth of the time for gravity settling. The time for the separation depends on input power to the ultrasonic transducer. With increasing the power, the separation improves. Volume of the emulsion was also varied at constant power input. The separation enhances with decreasing the emulsion volume. Thus, the power input per volume is an operating parameter for the separation.