Abstract: OBJECTIVE To establish an UFLC-MS/MS method for determining the concentration of zidovudine in placental perfusate fluid. METHODS Mirtazapine was used as the internal standard, and samples were precipitated with acetonitrile. Analysis of zidovudine and mitrazapine was carried out on a Synergi 4u Hydro-RP 80A column(50 mm×2.00 mm, 4 μm). Gradient elution occurred using 0.1% formic acid-methanol at a flow rate of 0.6 mL·min^-1. Detection was performed with multiple reaction monitoring using positive electrospray ionization: m/z 268.1/127.1 for zidovudine and 266.2/195.0 for mirtazapine. RESULTS Linearities were obtained from 25-5 000 ng·mL^-1. The recoveries were 90.5%-96.7%. The intra-day RSD and inter-day RSD were all <15%. And the analytes were proved to be stable. CONCLUSION This method can be used for the determination of zidovudine in placental perfusate fluid.