Sonochemical degradation of microcystins (MC) produced by microcystis in water and the influence of various ultrasonic parameters were studied. The results show that microcystins could be effectively degraded in ultrasonic fields. 150 kHz is the best ultrasound frequency for microcystins degradation, and the removal ratio of microcystins reached 70% after 20 min ultrasonic irradiation at 150 kHz and 40 W. Furthermore, ultraviolet irradiation strengthened the ultrasonic degradation of microcystins.