Abstract: Objective To establish a method for determining isofraxidin concentrations in Sarcandra glabra and Qingrexiaoyanning capsules with high-performance liquid chromatographic-mass spectrometry.Methods Isofraxidin was extracted from Sarcandra glabra and Qingrexiaoyanning capsules with acetic ether and chloroform,respectively,and separated by isocratic reversed-phase chromatography.The mass spectrometric system was operated in multiple reaction monitoring mode.A pair of ions:precursor ion m/z 223 with product ion m/z 162 were chosen for the quantification of the analyte.Results The retention time of isofraxidin was 6.60 min,and the calibration curve was linear over a concentration range from 484 to 9 680 ng/ml.The average recovery was 96.7% and RSD 4.49%,with detection limit of 1 ng/ml.Conclusion The method is rapid,selective and sensitive for determining isofraxidin in Sarcandra glabra and Qingrexiaoyanning capsules.