Abstract: The degradation of diethylstilbestrol ( DES) in aqueous solution by ultrasound ( US) - Fenton reagent progress, determination by LC- MS/MS was studied. The effect of treating factors including the concentration of DES, the reaction time, the reaction temperature, the pH value in solution, the ultrasound power and Fenton reagent was investigated.In the optimal conditions with the reaction temperature of 0℃, the pH of 3.0, the ultrasound power of 200W, the H2O2of 8% and FeSO4·7H2O of 0.2g /L in Fenton reagent, the degradation rate of DES in aqueous solution could reach up to 85% with the treatment time of 50min.DES degradation in the range 50⁶00μg /L followed first order kinetics.