An UPLC-QTOF/MS method for the simultaneous determination of xylazine and 2,6-dimethylaniline in blood and urine was developed.The samples were extracted with ethyl acetate-hexane（1∶1,by volume）,then separated on a C18 reversed-phase column and analyzed by ultra high performance liquid chromatography coupled with quadrupole-time of flight mass spectrometry with positive electrospray ionization interface operating in the full scan ion mode.By software,the target compound was confirmed by the comparison of theoretical accurate moleculer mass,isotopic pattern abundance and product ion characteristics.The limits of detection for xylazine in blood and urine were 0.2, 0.1 μg/L,respectively,and the limits of quantitation were 0.6,0.3 μg/L,respectively.The limits of detection for 2,6-dimethylaniline in blood and urine were 0.5,0.3 μg/L,respectively,and the limits of quantitation were 1.5,1.0 μg/L,respectively.The recoveries were between 72.5% and 87.8%,with RSDs of 6.8%-9.7%.This method is rapid,sensitive and reproducible,and thus is suitable for the accurate quantitation of xylazine and its metabolite residues in real blood and urine samples.