Micron-sized and nano-sized rutile titanium dioxide (TiO2,) powders were used as the catalysts for the sonocatalytic degradation of methyl parathion, an organophosphorus insecticide. The ultrasound of low power was used as an irradiation source to induce the catalytic activity of the rutile TiO2 particles. It was found that the degradation of methyl parathion sonocatalytically progressed more rapidly in the presence of TiO2, particles than only with ultrasonic irradiation in the absence of TiO2 catalyst. Moreover, the sonocatalytic activity of the micron-sized rutile TiO2 particles was obviously higher than that of nano-sized rutile TiO2 particles. The influences of reaction parameters, such as the species of TiO2 particles, methyl parathion concentration, TiO2 amount, pH value, ultrasonic intensity, ultrasonic frequency and temperature have been investigated and the optimal conditions for eliminating methyl parathion have been established. The processes of methyl parathion degradation have been monitored by high performance liquid chromatography (HPLC), ion chromatography and UV-vis spectra. The results showed that methyl parathion in aqueous solution was completely degraded to give simple inorganic ions, such as NO2-, NO3-, PO43-, SO42-, etc. The kinetics of the degradation of methyl parathion followed the first-order reaction. The degradation percentage of methyl parathion surpassed 95% within 80 min in the optimal experimental conditions. (c) 2007 Elsevier B.V. All rights reserved.