In this study, the quantitative analysis of saikosaponins from Radix Bupleuri in China was performed by high performance liquid chromatography. Saikosaponin-a and-d were converted completely into saikosaponin-b1 and -b2 by mild acid treatment. Distinctive measuring of these converted diene-saponins provided a rapid and selective method for the determination of saikosaponin-a and-d in commercial samples of Radix Bupleuri. The conditions of extraction and conversion of saikosaponins were optimized using orthogonal design L9 (34). The HPLC analysis was performed on ODS-C18 column with a flow rate of 1.0ml/min and detection wavelength of 250 nm. Well resolved chromatograms of saikosaponin-b1 and-b2 were obtained with an isocratic elution of ace-tonitrile:1%formic acid water (37.5:62.5). Calibration curves of saikosaponin-b1 and-b2 were linear in the range of 4.9-98.0