Abstract:A method for determining the residues of L-Hydroxyproline in dairy products was established by an ultra performance liquid chromatography tandem mass spectrometry.Samples was enzymatic digest of bovine，and ultrasonic extracted with ethyl acetate，and purified with HLB solid phase extraction cartridge，and separated by UPLC BEH C18column，and quantitative analysis was performed by the multi-reaction-monitoring（MRM）mode.The qualitative ion pair （m/z）was 132.1/86.2；the quantitative ion pair （m/z）was 132.1/68.3.The results showed that the recoveries were between 94.53%-98.42%，and the relative standard deviation were less than 7.3%；according to RSN=10，the limit of quantificationn was 5.0 μg/kg.