A high performance liquid chromatography-tandem mass spectrometry(HPLC-MS/MS) with isotope dilution was established for the determination of niclosamide(NIC) in water,sediment,fish muscle and skin in natural proportions and shrimp muscle.The water sample was extracted with ethyl acetate after alkalization treatment,and the other samples were extracted with acetonitrile containing 0.1% ammonia,and purified using C18 powder.The extracts were separated on a Thermo Hypersil Gold C18(150 mm×2.1 mm，5 μm) column with acetonitrile-water as mobile phase at a flow rate of 0.3 mL/min,then detected in selected reaction monitoring(SRM) mode and quantified by internal standard calibration curve method with the stable isotope marker of NIC(NIC-13C6) as internal standard.Results showed that good linearities for NIC in the samples were observed in the range of 0.2-200 μg/L,with their correlation coefficients(r2) not less than 0.999 5.The average recoveries for NIC in water at three spiked levels of 2.5,25 and 250 ng/L ranged from 90.5% to 109% with relative standard deviations(RSD) of 3.2%-11%.The limit of detection(LOD) and limit of quantitation(LOQ) for NIC in water were 1.0 ng/L and 2.5 ng/L,respectively.While for NIC in sediment,fish muscle and skin in natural proportions and Procambarus clarkii muscle,the average recoveries at three spiked levels of 0.5,5.0 and 50 μg/kg were in the ranges of 89.4%-113%,92.8%-110% and 94.1%-107%,with their RSDs of 46%-12%,2.8%-11% and 3.2%-9.3%,respectively.The LODs and LOQs were 0.2 μg/kg and 0.5 μg/kg,respectively.With high sensitivity,accuracy and selectivity,the present method is suitable for the determination of NIC residues in practical aquatic environmental water,sediment,fish and shrimp.