A simple and sensitive high-performance liquid chromatography-electro-spray ionization tandem mass spectrometry (LC-ESI-MS/MS) method was developed and validated to determine raddeanin A in rat plasma. After precipitation of rat plasma samples with methanol, chromatographic separation was achieved on a BDS Hypersil C18 column (100×2.1mm, 2.4μm) using the mobile phase consisted of acetonitrile and 2mM ammonium acetate with 0.05% formic acid (60:40, v/v). The detection was performed in a triple quadrupole tandem mass spectrometer by multiple reaction monitoring (MRM) mode using negative ionization. The transition monitored were m/z 895.6→455.0 for raddeanin A and m/z 359.3→329.0 for IS, respectively. The method was linear over the concentration range of 2-1000ng/mL for raddeanin A. The intra-day and inter-day assay variations were <9.46%, and the accuracy values were between -2.04% and -6.52% relative error. The extraction recovery of raddeanin A was more than 70%, and the relative matrix effect ranges from 108.52% to 112.36%. The validated method has been successfully applied to determine the pharmacokinetic profile of raddeanin A in rat plasma following oral and intravenous administration.