Abstract: A high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method was established for simultaneous determination of 6 β-lactam antibiotic residues in aquatic product.Samples were extracted with acetonitrile - water ( 15 ∶ 2 , v ∶ v ) and purified by Oasis HLB solid phase extraction column . Chromatographic separation was carried out on a C 18 column, the mobile phase was acetonitrile -0.01mol/L ammonium acetate solution ( pH4.5 ) with gradient elution , then residues were detected by MS / MS in the ESI (+) -MRM mode. Limits of detection for the method were 0.2～2μg/kg, recoveries ranged from 80.8%～92.9%, and relative standard deviations (RSD) were in the range of 2.6%～9.1% (n=9) . The method was accurate, sensitive, simple and suitable for the determination of six β-lactam antibiotic residues in aquatic product.