Various aspects of antioxidant activity in vitamin C were evaluated in this study. Relatively high level of 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity was detected in vitamin C, but not in non-antioxidative vitamin, vitamin B1. Vitamin C also reduced the production of lipid peroxidation in Chinese hamster lung fibroblast (V79-4) cells with IC50 value of 4μg/mℓ. Vitamin B1 showed comparable reduction in lipid peroxidation products (IC50 value was about 10μg/mℓ). It was shown that vitamin C also dose-dependently enhanced the activities of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPX) in V79-4 cells, and these effects were not observed in vitamin Bl-treated cells. Our data suggest that well-known antioxidant vitamin C involved in direct activation of SOD, CAT and GPX.