Objectives: Paeonia japonica has been widely used for gynecopathy and analgesic effects in Korean Traditional Medicine. The aim of the present study is to determine the antioxidant effect of Paeonia japonica extracts(PJE) by using mouse embryonic fibroblast cells(MEF cells). Methods: We evaluated Radical Scavenging Activity of PJE by the DPPH assay. Protective effect of the PJE on the hydrogen peroxide($H_2O_2$) induced oxidative damage of MEF cells was analyzed by the MTT assay. The Morphological changes of MEF cells induced by P. japonica, $H_2O_2$ and P. japonica+$H_2O_2$ was evaluated by DAPI staining. And effect of PJE on the rate of apoptosis in MEF cells was measured using flow cytometry with Annexin V-FITC and PI double staining. Results: We observed that PJE contain significant DPPH radical scavenging activity. Cell viability of oxidative damaged cells treated with various concentrations of $H_2O_2$ was increased by treatment with PJE. Flow cytometric analysis of the cells treated with $H_2O_2$ in the absence or presence of PJE showed that the crumbled G1 peak was accumulated by the treatment with $H_2O_2$ alone, but restored by addition of PJE. Portion of cells that undergo apoptosis mediated by oxidative stress was decreased by treatment of PJE. The nuclear fragmentation occurred in the oxidative damaged MEF cells was also decreased by PJE treatment. Conclusions: Taken together, our results suggest that PJE exhibits significant antioxidant activity and functions to inhibit cell death mediated by oxidative damage induced apoptotic pathways.