Abstract Abstract: A method was developed for the determination of monepantel and its metabolite residues in dairy products by high performance liquid chromatography -tandem mass spectrometric (HPLC–MS/MS). The sample was extracted with water, saturated sodium chloride solution and acetonitrile, and then purified by hexane. The target compounds were separated on an inertsil C8-3 column (2.1 mm×100 mm ，3μm) using a gradient elution program of methanol and 0.5 mmol/L ammonium acetate, and detected by tandem mass spectrometry in negative electrospray ionization and multiple reaction monitoring (MRM) mode. The quantification of monepantel and its metabolite residues was performed by the external standard method. The calibration curves showed good linearity in the concentration range of 0.1～5.0 μg/L with a limits of quantitation (LOQ) of 2.0 μg/kg. The recoveries in dairy products at three spiked levels were in the range of 79.5% -102.9% with relative standard deviations (RSDs) between 2.0% and 5.3%. With the advantages of convenience, fast, accurate ,high sensitivity, strong anti-interference capability and good recovery and repeatability, the method was suitable for the analysis of monepantel and its metabolite residues in dairy products.