Abstract:A method for simultaneous determination of chloramphenicol and dexamethasone residues in pork tissues by liquid chromatography-tandem mass spectrometry（LC-MS/MS）was established.The residues in pork samples were extracted by ethyl acetate and dried by nitrogen.The residues were dissolved and passed over the Silica columns，the eluents were dried by nitrogen and metered volume by initial flow.The liquid was performed on a Shim-pack GIST C18 chromatographic column with gradient elution of pure water and methanol.The mass spectrometry was carried out with multiple reaction monitoring，chloramphenicol was quantified by internal standard method and dexamethasone was quantified by external standard method.The separation and analysis of two target compounds was completed within 5 min.Chloramphenicol and dexamethasone showed good linear relationships in the concentration range of 0.2 μg/kg to 40 μg/kg with the correlation coefficients of 0.999 9 and 0.999 7 respectively.The recovery of chloramphenicol at 3 spiked levels（1，2.5，5μg/kg）was 90.54%-101.73%and the recovery of dexamethasone at 3 spiked levels（0.5，2.5，5 μg/kg）was 83.82%-87.5%.The standard deviations of the same batch and 3 batches were less than 10%（n=5），the quantitation limits of two target compounds were less than 0.15 μg/kg.