Abstract: A gas chromatographic-mass spectrometric method for determining oleanolic and ursolic acid has been developed.Trimethylsilyl derivatives of the acids were prepared with bis(trimethylsilyl)trifluoroacetamide(BSTFA) for gas-chromatographic separation on a DB-5 MS capillary column.The temperature program comprised two phases: initially the temperature was set at 100℃ for 2 min.It was then ramped to 300℃ at a rate of 10℃/min and held for 14 min.oleanolic acid and ursolic acid were comfirmed by comparison of both mass spectra and GC retention time with the standards.The quantitative analysis was based on the peak area.Excellent linearity was obtained over the range 4.1~102 μg/mL for oleanolic acid and 4.7~114 μg/mL for ursolic acid respectively.The recovery of the spiked oleanolic and ursolic acid was 77.1% and 89.4% respectively with acceptable RSD.