The degradation of trichloroacetic acid (TCA) was studied with ultraviolet (UV) photolysis, ultrasound (US) sonolysis and their combination. It was found that the degradation in the combined processes was more significant than in the UV photolysis or sonolysis alone. The effects of pH and dissolved gases on the rate of photosonochemical degradation of TCA were investigated and the degradation kinetics, mechanism and possible degradation products were discussed in detail.