A method for the simultaneous determination of nine perfluorocarboxylic acids (PFCAs) in water by precolumn derivatization. gas chromatography. electron capture detector (GC-ECD) was established. PFCAs were firstly converted to amide derivative products using 2,4. difluoroaniline (2,4-DFA) as derivatizing agent and N, N'-dicyclohexylcarbodiimide (DCC) as dehydrating agent. Then the amide derivative products were determined by ECD after separation with TR-5 capillary. column chromatography. The experimental conditions in derivatization of PFCAs were optimized, including the dosage of 2,4-DFA and DCC, reaction solvent, reaction temperature and reaction time. The optimal derivatization parameters were obtained. The results showed that the linear correlation coefficients of nine derivative products of PFCAs were higher than 0.99 under the optimized experimental conditions. The limits of detection were 0.62 - 1.38. mu g/L, while the relative standard derivations RSDs were 1.3% - 7.5%. The proposed method was applied to the analysis of PFCAs in municipal sewage. It was found that the municipal sewage contained trace PFCAs which mainly existed in the form of perfluoropentanoic acid (PFPeA), perfloroheptanoic acid (PFHpA) and pentadecafluorooctanoic acid (PFOA). The recoveries of actual samples were between 84.4% and 120.9%. The method was stable and reliable with low cost, and it could meet the simultaneous determination of several PFCAs in water samples. This study provided technical support for the pollution assessment of perfluorinated compounds in water.