Effect of the ultrasonic wave on microfiltration of yeast suspension was examined using a tubular ceramic module operated in cross-flow mode. Applied pressures (transmembrane pressure) were varied between 11.27-46.06 kPa. Feed flow velocities were studied in the range between 0.02-0.48 m/s. Feed concentrations were varied as 0.005, 0.010 and 0.020 g/cm[superscript 3]. Acoustic intensities were studied between 0.91-3.53 W/cm[superscript 2] at the frequency of 23.8 kHz. From the experiment, it is found that permeate flux of microfiltration coupling with ultrasonic irradiation was dependent with the feed flow velocity, the transmembrane pressure and the feed concentration. Cake removal induced by ultrasonic cleaning increased with increasing transmembrane pressure in the prior stage, and then decreased with the increase in applied pressure in the later stage due to the strong compaction of cake layer. Besides, it is shown that ultrasound has affected the increase of permeate flux at the lower feed flow velocity. Increase in sound intensity and sound frequency gave rise to the increase in ultrasonic cleaning performance. However, for a long period of sonication with high intensity, effect on the characteristics of the membrane was demonstrated. Observation of yeast cells after being irradiated at the highest acoustic power (40 w) at the controlled temperature of 30 C found no change in morphology, particle size distribution and cultivation capability. The economic analysis of the application of ultrasound into the conventional cross-flow microfiltration was also discussed. In the case that ultrasonic wave was introduced to microfiltration, the decrease in cake buildup over the membrane and the increase in permeate flux in the ratio of 1.5 to 3.0 were expressed compared to those obtained from microfiltration without ultrasound.