In the present research, microfiltration performance was remarkably improved by ultrasonic irradiation. It has been found that ultrasonically induced cavitation is effective for loosening and detaching the cake deposited on the surface of the membrane. Cross-flow microfiltration in a plate and frame module with Nylon 66 membrane was investigated using a model suspension containing baker's yeast. The factors affecting the steady-state permeate fluxes, i.e. the ultrasonic power, the transmembrane pressure, the feed velocity and the feed concentration, have been studied. The experimental results obviously showed that the suitable application of ultrasonic wave could enhance the flux up to 3 times that without ultrasonic wave. An optimum operating transmembrane pressure and the optimum ultrasonic intensity were found. In addition, the ultrasonic effect was more pronounced at a lower feed velocity and a lower feed concentration. It was confirmed that an increase of the steady-state flux was caused by a major reduction of the cake resistance.