A sensitive and rapid LC-MS/MS method was developed and validated for the determination of kadsurenone in rat plasma using lysionotin as the internal standard (IS). The analytes were extracted from rat plasma with acetonitrile and separated on a SB-C18 column (50 × 2.1 mm, i.d.; 1.8 µm) at 30 °C. Elution was achieved with a mobile phase consisting of methanol-water-formic acid (65:35:0.1, v/v/v) at a flow rate of 0.30 mL/min. Detection and quantification for analytes were performed by mass spectrometry in the multiple reaction monitoring mode with positive electrospray ionization m/z at 357.1 → 178.1 for kadsurenone, and m/z 345.1 → 315.1 for IS. Calibration curves were linear over a concentration range of 4.88-1464 ng/mL with a lower limit of quantification of 4.88 ng/mL. The intra- and inter-day accuracies and precisions were <8.9%. The LC-MS/MS assay was successfully applied for oral pharmacokinetic evaluation of kadsurenone using the rat as an animal model.