In recent years,the demanding of high quality dairy products raised obviously.However,the dairy products safety problems were widely concerned,due to the illegal additions have been detected frequently.The highly developed technology of LC-MS has become the main quantitative determination of methyl testosterone residues due to the high accuracy and low detection limit[1].In this abstract we developed a method to quantitative analyze the methyl testosterone residues in milk with high accuracy using isotopic dilution mass spectroscopy.