An ultra high performance liquid chromatographic(UPLC) method was established for the rapid determination of sulfamethoxazole(SMZ),N acetyl sulfamethoxazole(N-ac-SMZ) and trimethoprim(TMP) in fish tissues,including muscle and skin in natural proportions,liver,kidney,gill and plasma.Samples of muscle and skin in natural proportions,liver,kidney and gill tissues of fish were prepared using the modified QuEChERS,and plasma sample was prepared by a liquid-liquid extraction procedure.The analytes were separated on an Acquity UPLC-BEH C18 column(2.1 mm×100 mm，1.7 μm) with methanol and water containing 0.1%acetic acid as mobile phases,at a detection wavelength of 270 nm,using an absorbent minus median baseline filter(MBF) in data acquisition mode.The external standard method was used for quantitation.Results showed that there were good linear relationships for SMZ,N ac-SMZ and TMP in the range of 0.05-10 mg/L with correlation coefficients(r2) not less than 0.998 9.The detection limits and quantitation limits for the analytes in fish tissues were 25 μg/kg and 50 μg/kg,respectively.Recoveries for the target compounds at spiked levels of 0.05-2.00 mg/kg were between 68.2%and 97.3%with relative standard deviations of 1.7%-13%.The method is simple,accurate and highly sensitive,and is suitable for the residue determination,pharmacokinetic and tissue distribution study of SMZ,N-ac-SMZ and TMP in fish.