Volatile fatty acids(VFAs) are typical malodorous substances,which are at trace levels in the ambient air.A method of gas chromatography-mass spectrometry(GC-MS) was established for the simultaneous determination of seven VFAs ie.acetic acid,propanoic acid,isobutyric acid,butyric acid,acrylic acid,isovaleric acid and valeric acid in ambient air.Ambient air samples were firstly collected with impregnated silica gel tube,then ultrasonically extracted with ultrapure water,finally partitioned with methyl tert-butyl ether,concentrated and set to a certain volume.The target compounds were determined by GC-MS,and quantified by internal standard method.Results showed that the calibration curves for seven VFAs were linear(r2≥0.995) in their respective concentration ranges with the detection limits of 0.11-4.78 μg/m3.The recoveries were in the range of 62.3%-110% with relative standard deviations of 2.2%-12%.The method is simple,accurate and sensitive,and is suitable for the determination of VFAs in ambient air.