Abstract: Hollow fibre ultrafiltration membrane is frequently employed in the water treatment processes.However, the fouling of ultrafiltration membrane significantly affects the economics of the process.In this study the fouled polyvinylidenefluoride ultrafiltration membrane and its module were cleaned by flat ultrasonic treatment with 2000 mg·L^-1 citric acid.The cleaning results were determined by a cleaning ratio defined by the authors and SEM, and also validated by membrane flux.Ultrasound was shown to be beneficial to cleaning and the cleaning ratio was 80% with no damage of membrane and was 25% more than that without ultrasonic treatment.The optimal ultrasonic treatment parameters were: frequency 40 kHz,sound intensity 2200 W·m^-2,treatment time 30 min.For the fouled module, the flux increased from 0.0368 cm³·cm^-2·min^-1 to 0.1254 cm³·cm^-2·min^-1,i.e., the flux recovery was 72.5% of the new membrane without back purge and the flux was increased to 241% of the initial flux of fouled membrane.