A gas chromatography-mass spectrometric(GC-MS) method was developed for the simultaneous determination of 31 free fatty acids(FFAs) in plasma.By comparing and optimizing the extraction and derivatization of FFAs from plasma,a solution of chloroform ：methanol(1∶2,by volume) was selected to extract FFAs,and acetyl chloride was used for the FFAs derivatization before GC-MS detection.Results indicated that there were good linear relationships for 31 FFAs in their respective concentration ranges,with correlation coefficients(r) not less than 0.999 0.The limits of detection(LOD) and the limits of quantitation(LOQ) were in the ranges of 0.010-0.050 μg/mL and 0.034-0.167 μg/mL,respectively.When C13∶0 and C23∶0 were used as target compounds to valify the method,the average recoveries for plasma quality ranged from 86.3%-115%,with the intra-day RSDs(n=6) not more than 6.3% and the inter-day RSDs(n=3) not more than 7.8%.The developed method was applied to detect the FFAs in the plasma samples of 49 pregnant women.21-31 FFAs were detected in the plasma,among which C16∶0(palmitic acid),C18∶2n6c(linoleic acid),C18∶1n9c(oleic acid) and C18∶0(stearic acid) were the main fatty acids.With more fatty acids detected,smaller sample volume required,lower LOD and LOQ as well as better accuracy of qualitation and quantitation,the proposed method is more suitable for the analysis of FFAs spectrum in plasma.