OBJECTIVE： To establish a method for the concentration determination of novel insulin sensitizer ZG02 in liver microsomes of rats， and to study its metabolism stability in vitro. METHODS： ZG02 was respectively dissolved in phaseⅠincubation system of rat liver microsomes initiated by NADPH， in phase Ⅱ incubation system initiated by UDPGA and in two-phase incubation system initiated by NADPH and UDPGA. After incubated in 37 ℃ water bath for 0， 5， 10， 15， 20， 30， 45 min， the reaction was terminated. Using indometacin as internal standard， UPLC-MS/MS method was used to determine the concentration of ZG02. The determination was performed on Waters BEH C18 column with mobile phase consisted of water （0.01％ formic acid）-acetonitrile （0.01％ formic acid） （35 ∶ 65，V/V） at the flow rate of 0.4 mL/min. The column temperature was 35 ℃， and the sample size was 2 μL. The ion source was electrospray ion source and negative ion scanning carried out with multiple reaction monitoring mode. The ion pairs used for quantitative analysis were m/z 458.115 9→323.073 0 （ZG02） and m/z 356.069 0→312.080 4 （internal standard）， respectively. The residual percentage and enzyme kinetic parameters of ZG02， contribution rates of metabolic enzymes in different incubation systems were calculated with the concentration of ZG02 incubated for 0 min as reference. RESULTS： The linear range of ZG02 was 1-400 μg/L； the limits of quantitation and detection were 1 μg/L and 0.25 μg/L. RSDs of inter-day and intra-day were all lower than 10％， accuracies were 87.26％-94.58％. The extraction method and the matrix effect didn’t affect the determination of the tested substance. At 45 min of incubation， the residual percentages of ZG02 were （73.33±1.53）％ in phaseⅠ incubation system， （50.63±3.42）％ in phase Ⅱ incubation system and （45.81±2.56）％ in two-phase incubation system. Half-time period of phase Ⅰ incubation system， phase Ⅱ incubation system and two-phase system were 67.28， 30.26， 25.57 min； clearance rate were 20.60， 45.80， 54.20    μL/（mg·min）， respectively. The contribution rates of phase Ⅰ incubation system and phase Ⅱ incubation system were 38.01％ and 84.50％. CONCLUSIONS： Established UPLC-  MS/MS method is simple， rapid and specific. It can be used for the concentration determination of ZG02 and in vitro metabolism stability study in rat liver microsomes incubation system. The metabolism stability of ZG02 is moderate in phase Ⅰ and phase Ⅱ incubation systems， but poor in two-phase incubation system. The main metabolic reaction may be phase Ⅱ metabolic enzyme mediated glucuronization.