Abstract: A particle sizing method based on the principle of ultrasonic attenuation (UA) with three frequencies is presented. As a theoretical basis, the ECAH model is employed to analyze relationship between attenuations and particle size and concentration. Experiments are carried out to measure the particle size distribution (PSD) of aqueous glass beads suspensions with vol.5% concentration, in which ultrasonic signal has been generated and received by three transducers with fixed frequencies 1, 2 and 5MHz. Amplitude and attenuation can be obtained using FFT technique. The measured data are evaluated by both Philip-Twomey-NNLS algorithm and the modified Chahine algorithm to solve the first kind Fredholm integral equation and get the PSD and concentration. The ultrasonic measurement results show good consistence with those from microscopical measurement, which indicates the exact PSD and concentration can be obtained and equipment can be simplified by the promoted method.