The ultrasonic irradiation (28 kHz, 50W) in pre-cavitations regime was employed to enhance the degradation rate of styrene-acrylic acid copolymer in aqueous media with nano titania photocatalyst particles. A stainless steel cylindrical sono-photo reactor with capacity of about 1.25L, equipped with a UV lamp (250W) was used. The influence of operational parameters, i.e. catalyst concentration, pH and temperature was studied and the role of active species was also distinguished. For an initial substrate concentration of 30 mg L-1, under mild applied conditions of 30 mg L-1 of photocatalyst, 25 degrees C and natural pH, a degradation and mineralization conversion of 96% and 91%, respectively, was achieved using sono-assisted photocatalysis process in about only 60 min. These efficiencies are much higher than those obtained with only photocatalysis process. Meanwhile, the threshold of cavitations was found corresponded to catalyst concentration of about 70 mg L-1. Kinetic studies based on Langmuir-Hinshelwood and power law models in addition to the results from radical scavenger usage revealed that for sono-assisted process, the substrate undergoes degradation mainly via electron-hole redox on the surface of titania particles. It is while for the only photocatalysis process, the reaction proceeds via hydroxyl radicals in the solution bulk. (C) 2010 Elsevier B.V. All rights reserved.