Abstract: This study is to report the establishment of an UPLC-MS/MS method for the determinationof plasma concentration of UA carried in self-microemulsifying drug delivery system (SMEDDS) and its pharmacokinetics in rats.It was used for determination and analysis when serum with internal standard was extracted from C₁₈ solid-phase column.Acquity UPLC BEH C₁₈ column (100 mm × 2.1 mm, 1.7 μm) was used for separation.The mobile phase was acetonitrile - 0.1% ammonia with gradient elution at the flow rate of0.2 mL·min^-1.The column temperature was 40 ℃ and the detection wave length was 210 nm.It was detected by negative ion using electrospray ionization source (ESI) and scanned by multiple reaction ion monitoring (MRM) mode.The liner relationship of UA was very good in the range of 1.19 - 3 815.00 ng·mL^-1 (r = 0.999 0).Recovery rate of different concentrations were 87.42% - 89.95%.The precision of inter-day and intra-day were less than 11%.The method developed in our study was proved to be sensitive, rapid and simple.It is suitable for the pharmacokinetic study of UA-SMEDDS in rats.