Abstract: Objective：To establish an UPLC-MS/MS method for determining the concentration of ibuprofen in rat plasma. Methods：The UPLC system was performed on a Agilent ZORBAX Eclipse Plus C18（2.1 mm×50 mm，5 μm）column with a mixture of 0.01% formic acid-0.05% ammonium formate aqueous solution and acetonitrile as mobile phase，the flow rate was 0.3mL·min-1， the column temperature was 40 ℃ and the injection volume was 5μL. The MS system was performed using multiple reaction monitoring(MRM) and electrospray ionization in negative mode， with the nebulizer pressure being 40 psi， the flow of drying gas being 6.0 mL·min-1， the temperature of drying gas being 150 ℃， the flow of sheath gas being 10.0 mL·min-1，the temperature of sheath gas being 175 ℃， the gas being high purity nitrogen， and the ion source voltage being 3 800 V. Results： A good linearity was obtained in concentration range of 20.477 1～2 047.71 ng·mL-1 of ibuprofen and the average recovery was 115%. Conclusion：The method was fast, simple, specific and sensitive. It can provide a theoretical basis for the research of quality standards of ibuprofen.