Objective:To observe the protective effects of genistein(GST) on the medulla oblongata neurons in ovariectomized rats. Methods:Rats with bilaterally ovariectomized were injected genistein 200 ?g/(kg?d) for 6 weeks. The madlondialdehyde(MDA)and superoxide dismutase(SOD)activity of medulla oblongata were measured, and the ultrastructure of medulla oblongata neurons were observed. Results:In the GST group,the MDA activity was reduced and SOD activity was increased compared with the OVX group. The ultrastructure of medulla oblongata neurons showed pathological changes in OVX group. These ultrastructure was not find in GST group. Conclusion:GST could protect neurons of medulla oblongata, which might be related to eliminate oxygen free radical.