The ultrasound effect applied on potassium dihydrogen phosphate was investigated in a continuous crystallization system. The studied process variables were ultrasonic power (W) and residence time. The crystal size distributions of the final products obtained with and without ultrasonic power were determined and the data were evaluated by using modified form of Abegg. Stevens and Larson (ASL) model. The supersaturation limit decreased with ultrasonic waves and the crystal morphology was modified. The average crystal size decreased in the presence of ultrasonic power. An abrasive effect was observed at a high ultrasonic power input. (C) 2010 Elsevier B.V. All rights reserved.