An analytical method was established for the confirmation and quantitation of short chain carboxylic acids in aged transformer oil by gas chromatography-tandem mass spectrometry（GC-MS）and high performance liquid chromatography with dispersive liquid-liquid microextraction（DLLME/HPLC）.The short-chain carboxylic acids in aged transformer oil were detected by GC-MS using N,O-bis-（trimethylsilyl）-trifluoroacetamide（BSTFA）as silane derivatization reagent,and formic acid,acetic acid and furoic acid in transformer oil were quantified by DLLME/HPLC.After extracting carboxylic acid in transformer oil with acetonitrile as extractant,BSTFA was added into the extraction phase of acetonitrile for silylation derivatization.After 60 min of the reaction at 60 ℃,the samples were determined by GC-MS.Results showed that 14 kinds of short chain carboxylic acids were detected in heat aged transformer oil,including formic acid,acetic acid and furoic acid.The formic acid,acetic acid and furoic acid in the standard oil sample were extracted with water as extractant which was directly taken for injection.The calibration curves of formic acid,acetic acid and furoic acid in the transformer oil were linear in the ranges of 0.05-50.0 mg/L,0.05-50.0 mg/L and 0.01-2.0 mg/L,respectively,with correlation coefficients（r） more than 0.998.The limits of detection（LOD） of the method were 36.1，47.3 and 7.0 μg/L,with relative standard deviations（RSD） of 2.4%,3.3% and 3.6%,respectively.The enrichment factors for the three carboxylic acids were within the range of 8-10 times.The recoveries for the aged oil samples ranged from 91.7%to 107%.The proposed method is simple and effective,and provides analytical data for the correct use of aged characteristic quantity of transformer oil paper insulation and study on effect of carboxylic acid on aged oil paper insulation.