Abstract: A method of GC with internal standard method for the determination of pentachlorophenol (PCP) in aquatic products was proposed. The sample of aquatic product was extracted with n-hexane, and the extract obtained was back extracted with K2CO3 solution. The pentachlorophenol in the K2CO3 solution was then derivatized with acetic anhydride, and the derivatized product was determined by GC. The tribromophenol was selected as internal standard. Linear relationship of pentachlorophenol was kept in the range of 0.5-50.0 μg·L-1, with detection limit (3S/N) of 1.0 μg·kg-1. The proposed method was applied to the analysis of aquatic products, giving values of recovery and RSD′s (n=6) in the ranges of 81.0%-96.4% and 3.7%-9.3% respectively.