Ginseng has an anti-cancer effect in several cancer models. This study was to characterize active constituents of ginseng and their effects on proliferation of prostate cancer cell lines, LNCaP and PC3. Cell proliferation was measured by $[^3H]$thymidine incorporation, the intracellular calcium concentration by a dual-wavelength spectrophotometer system, effects on mite-gen-activated protein (MAP) kinases by Western blotting, and cell attachment and morphologic changes were observed under a microscope. Among 11 ginsenosides tested, ginsenosides $Rg_3;and;Rh_2$ inhibited the proliferation of prostate cancer cells. $EC_{50}s;of;Rg_3;and;Rh_2$ on PC3 cells were $8.4{mu}M;and;5.5{mu}M$, respectively, and $14.1{mu}M;and;4.4{mu}M$ on LNCaP cells, respectively. Both ginsenosides induced cell detachment and modulated three modules of MAP kinases activities differently in LNCaP and PC3 cells. These results suggest that ginsenosides $Rg_3;and;Rh_2$-induced cell detachment and inhibition of the proliferation of prostate cancer cells may be associated with modulation of three modules of MAP kinases.