To investigate effect of caffeic acid on the intracellular reactive oxygen species production, we used DHE for intracellular superoxide anion production, DCF for intracellular ${H_2}{O_2}$ production and DHR for intracellular hydroperoxide production in Raw 264.7 cells. DPPH assay showed that antioxidant activity of caffeic acid with 39.5 ${mu}M$ of ${IC}_{50}$ values was similar to that of ascorbic acid with 41.3 ${mu}M$ of ${IC}_{50}$ values. Caffeic acid dose-dependently inhibited silica-induced ${H_2}{O_2}$ and hydroperoxide production but did not affect superoxide anion production in Raw 264.7 cells, which suggest that antioxidant effect of caffeic acid acts on the post-step of superoxide anion. On the other hand, caffeic acid showed a potent antioxidant effect in $lCuSO_4$-induced lipid peroxidation. Furthermore, plasma superoxide dismutase activity (3.43${pm}$0.23 U/ml) in 10 mg/kg caffeic acid-fed mice was significantly higher than that (2.32${pm}$0.24 U/ml) of control. From the above results, it is referred that caffeic acid appears to have potent anti-oxidant activity in both cell system and in vivo system.