Detailed surface characteristics of the particles produced during cavitation erosion may well be significant in monitoring the cavitation erosion progress. Utilizing computer image analysis techniques, the size and shape factor for particles of Al-99.999 were analysed. The particle morphology features were also clarified. In incubation period, The particles have distinctive characteristics which differed from that for the subsequent periods. These characteristics include the value of longitudinal ratio and roundness factor, limit size range and morphological features such as lamella shape, folding, curving and one of the particle surfaces was the virgin surface. In acceleration, steady-rate and attenuation period, the particles have a wide size range and larger thickness compared with that for the incubation period. The maximum particle size was in acceleration and steady-rate period, and it was about 360 µm. For all the cavitation erosion rate periods, the particles were out of sphericity and they have a roundness factor larger than 2. The particle generation mechanism is fatigue failure.