Abstract: To investigate the neuroprotective effect of estrogen on the H2O2-induced oxidative stress in PC12 cells,oxidative damaged PC12 cells was treated by H2O2 to construct the model on the oxidative stress reaction,and estrogen was added as a pretreatment to protect the cells.The survival rate of the cells was determined by MTT method,intracellular ROS generation was detected by DCFH-DA fluorescent probe,apoptosis was analyzed by Hoechst/PI fluorescence staining,and the level of mitogen-activated protein (MAP) kinase phosphorylation was detected by the Western blotting.The results showed that:The pretreated pheochromocytoma cell line PC12 by estrogen (0.001—1μmol/L) recovered significantly from the hydrogen peroxide (H2O2)-induced cell injury.The intensity of DCFH-DA fluorescence was significantly increased after the treatment by H2O2,indicating that ROS generation was successfully induced in PC12 cell,and estrogen (1μmol/L) decreased the DCFH-DA fluorescence intensity significantly.Estrogen suppressed H2O2-induced phosphorylation of p38MAPK and increased H2O2-induced phosphorylation of ERK1/2.It was suggest that estrogen protected against H2O2-induced oxidative stress in vitro and its protective effect was associated with the inhibition of p38 MAPK and the activation of ERK.