A method of HPLC-MS/MS with internal standard for the determination of L-carnitine in dairy products was developed.After the sample was dissolved in 0.1 mol/L HCl solution and its protein was precipitated with acetonitrile,the object was separated with a HILIC chromatographic column,tested by HPLC-MS/MS with sheath flow electro-spray ionization under positive ion scanning and multiple reaction monitoring(MRM) mode,and quantified by the internal standard method.The average recoveries at three spiked levels were in the range of 85.2%-102.0% with RSDs(n=6) of 7.6%-14.3%.The limit of detection (LOD) was 50 μg/kg and the limit of quantitation(LOQ) was 200 μg/kg.The proposed method was applied in the analysis of several real samples of different origins from overseas,and 20 samples were screened for L-carnitine with content range of 68-165 mg/kg,of which only 1 sample did not match with the label.This method was rapid,simple and accurate,and was suitable for the determining of L-carnitine content in dairy products.