Abstract: This study focused on the degradation of one of organophosphorus pesticides triazophos by an ultrasonic/H2O2 system and the factors including ultrasonic power,initial concentration of triazophos and p H value of aqueous solution on the degradation were investigated. Results indicated that the ultrasonic/H2O2 system was effective in the degradation of triazophos in aqueous solution and had a noticeable synergetic effect in the removal of triazophos compared with the single treatment of ultrasonic and H2O2. Furthermore,the degradation efficiency of triazophos was significantly improved as ultrasonic power increased from 475 W to850 W. In addition,the degradation efficiency declined as the initial concentration of triazophos increased from2 mg/L to 20 mg/L under ultrasonic/H2O2 treatment. It was also found that the degradation of triazophos was strongly p H-dependent and alkalinity condition favored the degradation. The degradation efficiency was 79.2%when the ultrasonic treatment was operated at 300 W for 90 min with p H value of 9 with the concentrations of triazophos and H2O2 at 2.46 mg/L and 2.5 g/L,respectively. The degradation kinetics of triazophos was fitted to the first-order kinetics model well.