The metabolism of ginseng saponins by human intestinal bacteria was studied using human feces under anaerobic culture conditions. $Ginsenoside-Rb_1$, $-Rb_2$ and -Rc(protopanaxadiol type) were mainly metabolized to compound-K(C-K), $20-O-[{alpha}-L-arabinopyranosyl(1{ ightarrow}6)-{eta}-{_D}-glucopyranosyl]-20(S)-protopanaxadiol(compound-Y,;C-Y)$, $20-O-[{alpha}-L-arabinopyranosyl(1{ ightarrow}6)-{eta}-{_D}-glucopyranosyll-20(S)-protopanaxadiol(ginsenosied-MC,{;}MC)$, respectively, and $ginsenoside-Rg_1$ and -Re(protopanaxatriol type) to their aglycon, 20(S)-protopanaxatriol, though the pathway and rate of the metabolism were affected by fermentation medium. C-K was not decomposed any more, while C-Y and Mc were both gradually hydrolyzed to C-K.