Abstract: The paper presents the acoustic method of detection and determination of radius distribution of the microbubbles suspended in water. The basic idea of the method consists in forcing microbubbles to grow and then to collapse. While the bubbles collapse the audible signal is recorded and analysed. Each descending bubble generates a pressure pulse that can be counted. Cavitation growth and collapse of the microbubble are the consequences of the dynamic pressure changes in flowing water. The critical pressure that causes the cavitation inception remains in relation with the microbubble radius. Thus the initial radius distribution can be obtained by counting of the pressure pulses recorded for systematically changed critical pressure. The paper contains the description of the device for microbubbles radius distribution based on the method. The main part of device is the nozzle with internal element. The examples of measurements performed with the use of the device are included.