Abstract: A quantitative method for epimedin A, B, C and icariin in rat plasma was established using LC-MS/MS after intermuscular administration of Chuankezhi injection to rat. Chromatographic separation was performed on an Agilent Eclipse XDB-C₁₈ column (150 mm×2.1 mm, 5.0 μm) at 40℃. Mobile phase consisted of acetonitrile -0.1% formic acid in water (35:65), and the flow rate was 0.22 mL·min^-1. The LC effluent was detected and analyzed using an ESI-triple quadrupole tandem mass spectrometer under the multiple reaction monitoring (MRM) in the negative ion mode. The plasma samples were treated with solid phase extraction prior to LC-MS/MS analysis. As a result, all of the four analytes displayed a good linearity over the concentration of 1-1000 ng·mL^-1. The RSDs of intra-day and inter-day assays were less than 5.99% and 10.16%, respectively. The relative recovery of each analyte was between 88.1%-101.1% with RSD<7.9% and the absolute recovery was between 72.0%-86.6% (RSD<6.3%). In conclusion, the established method shows good specificity, sensitivity and efficiency for quantifying the four flavonoid glycosides contained in rat plasma.