Abstract: An analytical method was established to determine metolcarb in paddy soil,paddy water,rice straw,rice hull and brown rice by ultra high performance liquid chromatography tandem mass spectrometry(UPLC-MS/MS).Metolcarb residues in rice samples were extracted by acetonitrile and subjected to a salting-out procedure.The samples were further purified by N-propyl-ethylenediamine(PSA) and white carbon black(SiO2·nH2O),then analyzed by UPLC-MS/MS in the mode of multiple reaction monitoring.The linearity was satisfactory in the concentration range of 0.005-1 mg/L, with a correlation coefficient r>0.98.When metolcarb was spiked at 0.01-5 mg/kg level in soil matrix and at 0.005-1 mg/L level in water matrix,the average recoveries of metolcarb in different matrices varied from 76.7% to 107.8%,the relative standard deviation (RSD) varied from 1.7% to 8.5% and the method limit of detection (LOD) was 2.0×10-13 g.Moreover,the limit of quantification (LOQ) in paddy soil,rice straw,rice hull and brown rice were 0.01 mg/kg and 0.005 mg/L in paddy water.The developed method was applied for terminal residue study.When metolcarb was applied for two and three times at the recommended dose of 1.5 times(45 g/hm2,a.i.),the finial residues in brown rice was not detected (lower than 0.01 mg/kg),at the sampling intervals of 10 d,14 d and 21 d after the last application.