Ginsenosides are major components in Panax ginseng and known to have numerous pharmacological activities such as anti-cancer, anti-diabetes, anti-viral and anti-atherosclerosis effects. In this study, the regulatory activities of G-Rg3 and its derivative 25-hydroxy Rg3 (G-Rg3-2H) on the production of nitric oxide (NO) in macrophages and the proliferation of lymphocytes prepared from spleen and bone marrow under treatment of lipopolysaccharide (LPS) or concanavalin (Con) A were examined. G-Rg3 and G-Rg3-2H dose-dependently inhibited NO production from LPS-activated RAW264.7 cells and in agreement, these compounds protected RAW264.7 cells from LPS-mediated cytotoxicity. In contrast, G-Rg3-2H dose-dependently inhibited lymphocyte proliferation induced by both LPS and Con A, while there was no inhibition by G-Rg3. Therefore, our data suggest that these compounds may be applied for NO-mediated or lymphocyte-mediated immunological diseases.