Objective: To establish an effective method for simultaneously determining the concentration of brucine and strychnine in rat plasma by HPLC. Method: The processed rat plasma samples were separated on a Kromasil C18 column. The mobile phase consisted of acetonitrile-0.01 mol ·L-1 sodium heptane sulfonate and 0.02 mol ·L-1 potassium dihydrogen phosphate

adjusted pH to 2.8 with 10% phosphonic acid (24 ∶76). The detection wavelength was set at 264 nm. Result: Chromatograms showed endogenous peaks not interfering with the analysis. The calibration curves of brucine and strychnine were both in good linearity within the range of 50-2 000 μg ·L-1. The mean extraction recoveries were more than 86% while the precisions were less than 8%. The results of stability experiment meet certain requirements for the biopharmaceutical analysis. Conclusion: The method with good sensitivity and precision is applicable to the pharmacokinetic studies of the main compounds in total alkaloids from seeds of Strychnou nux-vomica .