Ultrasound (US) cleaning technique was applied to remove fouling of ultrafiltration (UF) and microfiltration (MF) membranes which were used to treat peptone and milk aqueous solutions, respectively. Membrane operations were performed by cross-flow filtration with 60 kPa operating pressure in an US field. The US employed had 28, 45 and 100 kHz frequency with 23 W/cm(2) output power. For each polymeric membrane made of polysulfone UF and cellulose MF, cleaning experiments were carried out with and without US after fouling. The fouled UF and MF membranes showed volume flux decline, but the membrane property was recovered by US irradiation. It was found in 28 kHz frequency that water cleaning was effective for recovery of declined condition due to fouling. Also, US-enhanced permeability of membranes was discussed in both membrane systems. We observed that US decreased the fouling condition in both membrane systems when US was irradiated before fouling. It was found that 28 kHz frequency US could enhance formation of the fouled layer in both filtration systems of peptone and milk solution.