Abstract: GC with headspace-solid phase micro-extraction (HS-SPME) was applied to the determination of 6 fatty acids, i.e., acetic acid, propionic acid, butyric acid, pentanoic acid, isopentanoic acid and hextanoic acid, in waste water. To attain a higher efficiency in SPME, the polar 85 μm PA coating was selected for the micro-extractor, and the extraction was carried out at 25 ℃ for 20 min from the sample solution having the acidity of pH 1.5, and with addition of 3.5 g of NaCl to 20 mL of sample solution as salting out agent. The analyte were separated with Stabilwax-DA capillary column and detected by FID. Linear relationships between values of peak area and mass concentration of 6 fatty acids were kept in definite ranges. Values of RSD′s (n=10) of the 6 fatty acids found were less than 10.0%.