We investigated the effects of melatonin administration on ovariectomy-induced oxidative toxicity and N-methyl-D: -aspartate receptor (NMDAR) subunits in the blood of rats. Thirty-two rats were studied in three groups. The first and second groups were control and ovariectomized rats. Melatonin was daily administrated to the ovariectomized rats in the third group for 30 days. Blood, brain cortical and hippocampal samples were taken from the three groups after 30 days. Brain cortical, erythrocyte and plasma lipid peroxidation (LP) levels were higher in the ovariectomized group than in controls, although the LP level was decreased in the ovariectomized group with melatonin treatment. Brain cortical and plasma concentrations of vitamins A, C and E as well as the NMDAR 2B subunit were lower in the ovariectomized group than in controls, although, except for plasma vitamin C, they were increased by the treatment. Brain cortical and erythrocyte reduced glutathione (GSH) levels were lower in the ovariectomized group than in controls, although erythrocyte GSH levels were higher in the melatonin group than in the ovariectomized group. Brain cortical and erythrocyte glutathione peroxidase activity and NMDAR 2A subunit concentrations were not found to be different in all groups statistically. Oxidative stress has been proposed to explain the biological side effect of experimental menopause. Melatonin prevents experimental menopause-induced oxidative stress to strengthen antioxidant vitamin and NMDAR 2A subunit concentrations in ovariectomized rats.