The ultrasonic degradation of the water-soluble polymers pullulan, poly(ethylene oxide) and polyvinylpyrrolidone was studied at a frequency of 500 kHz. The apparent degradation rate constants are 0.030 for pullulan, 0.076 for poly(ethylene oxide) and 0.032 min(-1) for polyvinylpyrrolidone. The degradation mechanism was analysed by using Glynn’s model. The water-soluble polymers used here are degraded with a Gaussian probability by ultrasonic irradiation.