The antioxidant activities of fermented red ginseng (FRG) were investigated in vitro and in vivo. The contents of total polyphenol and total flavonoid in FRG extracts were $17.01{pm}2.00$ ${mu}g/mg$ and $18.42{pm}3.97$ ${mu}g/mg$, respectively. These extracts were capable of directly scavenging ${alpha}$, ${alpha}$-diphenyl-picrylhydrazyl free radicals. The antioxidative effects of the FRG extracts in streptozotocin (STZ)-induced diabetic rats were also investigated. The activities of plasma alanine transaminase, aspartate transaminase, and ${gamma}$-glutamyltransferase were significantly decreased by extract administration as compared to an STZ control group. Hepatic glutathione content depleted by STZ treatment was significantly increased by treatment of the FRG extracts, but the elevation of lipid peroxide content induced by STZ was significantly decreased by the extracts. Activities of superoxide dismutase, catalase, glutathione peroxidase, and glutathione reductase decreased after STZ-treatment were recovered by the treatment of the FRG extracts. These results indicate that FRG extracts have antioxidative effets in STZ-induced diabetic rats.