Photochemical degradation and relative toxicity reduction of agricultural wastewater contaminated with methyl 1-[(butylamino)carbonyl]-1H-benzimidazol-2-ylcarbamate (benomyl) by the sonophotocatalytic system was compared with that of the photocatalytic system. Under the optimal conditions, i.e., initial benomyl concentration was 3.2 mg/l, the concentration of TiO2 was 2 g/L and H2O2 concentration was 1.5 mM, the degradation rates with a sonication/UV/TiO2 system was about 1.5 times higher than with a UV/TiO2 system and sonication/UV/TiO2/H2O2 system was about 1.3 times higher than with a UV/TiO2/H2O2 system, respectively. Furthermore, the relative toxicity with a sonophotocatalysis was about 18% lower than with a photocatalysis within a reaction time of 120 min. (C) 2009 Elsevier B.V. All rights reserved.