The ultrasonic degradation of poly(vinyl acetate) was carried out in the presence of an oxidizing agent, benzoyl peroxide. The time evolution of the molecular weight distribution (MWDs) was determined by gel permeation chromatography. A mechanism based on radical reactions is proposed. The rate coefficients for these reactions were determined by analyzing the MWDs by continuous distribution kinetics. A stoichiometric kernel that accounts for preferential mid-point breakage of the polymer chains was used. The degradation rate coefficient of the polymer decreased with increasing benzoyl peroxide concentration, as predicted by the model. © 2001 Elsevier Science Ltd.