An ultrahigh performance liquid chromatography-tandem mass spectrometric (UPLC-MS/MS)method was established for the determination of flufenacet in rats urine and feces.The urine and feces samples were extracted with acetonitrile.Chromatographic separation of the target compound was performed on a C18 column(50 mm×46 mm,5 μm) using ultrapure water containing 01% formic acid and acetonitrile as mobile phases at a flow rate of 06 mL·min-1.The detection of flufenacet was carried out by MS with electrospray ionization in positive ionization under multiple reaction monitoring mode.There were good linear relationships for flufenacet in rats’ urine and feces over the concentration ranges of 010-100 mg/L and 025-500 mg/L,with their correlation coefficients(r) larger than 099.The limits of quantitation for flufenacet in urine and feces were 010 and 025 mg/L,respectively.The intra RSDs and inter RSDs for the QC sampes were not more than 99%.The stability for flufenacet in urine ranged from 937% to 108%,and the recoveries and matrix effects were in the ranges of 970%-988% and 988%-107%,respectively.All the results met the requirements for bioanalytical method validation.The excretion kinetics in rats was also investigated after oral administration of flufenacet at a dosage of 400 mg/kg by body weight.The total accumulated excretion rate for flufenacet in urine and feces was 1262% in 144 h,in which the excretion percentages for urine and feces were 112% and 1013%,respectively.Results indicated that flufenacet was mainly excreted through feces.This method has the advantages of high sensitivity,selectivity and accuracy,and could be applied in the analysis of flufenacet in rats urine and feces.