The pharmacokinetic profi les and sulfamethoxazole(SMX) acetylation process in turbot reared at 18°C were investigated. Either SMX(parent drug) or its acetylized metabolite, N4-acetylsulfamethoxazole(Ac SMX), was administered intravascularly to turbot at a dosage of 50 mg/kg BW. Serum concentrations of the parent drug and its metabolite were both measured by HPLC, and the changes in concentration over time were analyzed in two- and non-compartment models because SMX treatment produced multiple peaks. The results demonstrated that the elimination half-life of the parent drugs, SMX and Ac SMX, were 159.2 and 5.9 h, respectively. The apparent volume of distribution was 0.2 and 0.8 L/kg, and the clearance was 0.038 and 0.222 L/(h·kg), for SMX and Ac SMX, respectively. SMX acetylation in turbot was 2.8%, and the deacetylation of Ac SMX was 0.2%. These fi ndings may be useful in optimizing SMX dosage regimens in turbot aquaculture. The pharmacokinetic profi les and sulfamethoxazole (SMX) acetylation process in turbot reared at 18 ° C were investigated. Either SMX (parent drug) or its acetylized metabolite, N4-acetylsulfamethoxazole (Ac SMX), was administered intravascularly to turbot at a dosage of 50 mg / kg BW. Serum concentrations of the parent drug and its metabolite were both measured by HPLC, and the changes in concentration over time were analyzed in two- and non-compartment models because SMX treatment produced multiple peaks. The results demonstrated that the elimination half-life of the parent drugs, SMX and Ac SMX, were 159.2 and 5.9 h, respectively. The apparent volume of distribution was 0.2 and 0.8 L / kg, and the clearance was 0.038 and 0.222 L / (h · kg) SMX and Ac SMX, respectively. SMX acetylation in turbot was 2.8%, and the deacetylation of Ac SMX was 0.2%. These fi ndings may be useful in optimizing SMX dosage regimens in turbot aquaculture.