Abstract:An analytical method for determination of dexamethasone in milk powder by high performance liquid chromatography-mass spectrometry/mass spectrometry had been established.The sample was extracted by ultrasonography with acetonitrile formate solution and purified by Oasis PRiME HLB solid-phase extraction column.Chromatographic conditions used Waters XBridge C18 column （2.1 mm ×150 mm，5 μm）and using 0.1 % formic acid water-acetonitrile as the mobile phase at a flow rate of 0.3 mL/min，with the column temperature at 40 ℃.Then dexamethasone was detected with ESI+.The detection limits of substance was 1.0 μg/kg，the limit of quantitative detection was 3.0 μg/kg.The calibration curves was linear in the range of 0-20 ng/mL，while the recovery rates was 90.7%-98.9%.The method was simple and high－efficient，repeatable and could be used for the determination of dexamethasone in milk powder.