To establish a rapid method of pentachlorophenol in aquatic products by GC-MS.Methods Sodium pentachlorophenol in the samples were converted to pentachlorophenol in acidic condition. Then they were detected by GC-MS, after the extraction, reextraction, derivatization with n-hexane, potassium carbonate, acetic anhydride, respectively. Results Pentachlorophenol showed a good linear relationship at a range of 0-100 μg/L, correlation coefficient r=0.999 1, with lower limit of determination (S/N=10) of 1.04 ng/g. Tests for recovery and precision were made at 3 concentration levels, giving results of average recovery in the range of 94% to 103%, with values of relative standard deviation RSD (n=6) in the range of 1.83%-3.82%.Conclusion The established method is rapid, simple and accurate. It can be used to rapidly determine pentachlorophenol in aquatic products.