An analytical method was developed for the simultaneous determination of 38 antibiotics residues in 5 classes of drugs,including sulfonamides,quinolones,tetracyclines,chloramphenicols and macrolides in milk by ultra-high performance liquid chromatography-tandem mass spectrometry(UPLC-MS/MS).The samples were extracted with acetonitrile containing 0.5%(by volume) formic acid,and cleaned up with an Oasis PRiME HLB solid phase extraction column.The target components were separated using an Acquity UPLC HSS T3 column(100 mm×2.1 mm i.d.,1.8 μm),then identified and quantified by UPLC-MS/MS with electrospray ion source(ESI) under multi-reaction ion monitoring(MRM) mode.Results showed that 38 antibiotics had good linear relationships in their respective linear ranges with correlation coefficients(r2) higher than 0.99.The limits of quantitation for 38 antibiotics were between 0.10 μg/kg and 1.0 μg/kg.Average recoveries for 38 antibiotics in milk at spiked levels of 1.0,5.0,10.0 μg/kg ranged from 70.7%to 94.9%,with relative standard deviations(RSD,n=6) of 4.0%-9.4%.With the advantages of easy operation,high sensitivity and good reproducibility,the method was applicable for the determination of antibiotics residues in milk.