Ginsenoside compound-K content in ginseng is very low, while it is the main intestinal bacterial metabolite and the final absorption style of the major components, such as ginsenosides Rbl and Rb2. The determination of ginsenoside compound-K in the fermentation liquor of ginseng saponins by reversed-phase high performance liquid chromatography was established. The separation was carried out under the following conditions: a Waters Symmetry C18 column (4.6 mm i.d. x 150 mm, 5 microm) was used at 35 degrees C with acetonitrile-water (48:52, v/v) as mobile phase at a flow rate of 1 mL/min. UV detection wavelength was set at 203 nm. The experimental results showed a good linear relationship between the peak area and mass concentration for ginsenoside compound-K within the range of 0.05-0.8 g/L (r = 0.9998). The relative standard deviation of peak area (n = 6) was 2.20%. The lowest detection limit (S/N = 3) was 2.5 mg/L. The average recoveries (n = 3) for the culture broth of ginseng saponins and notoginseng saponins were 98.6% and 99.7%, respectively. The method is rapid, simple, accurate and reproducible and can be utilized for the research and development of ginsenoside compound-K in pharmaceutical industry.