Abstract: Objective To explore the protection of magnesium sulfate (MgSO₄) on radiationinduced acute brain injuries. Methods 60 maturity Sprague-Dawley (SD) rats were randomly divided into 3 groups:blank control group, experimental control group and experimental-therapeutic group. The whole brain of SD rats of experimental control group and experimental-therapeutic group was irradiated to a dose of 20Gy using 6 MeV electron. MgSO₄ was injected intraperitoneally into the rats of experimental-therapeutic group before and after irradiation for five times. At different time points ranging from the 1 d, 7 d, 14 d, 30 d after irradiation, the brain tissue were taken. The xanthine oxidase and colorimetric examination were used to measure the superoxide dismurtase (SOD) and malonyldialdehyde (MDA) respectively in the rat brain respectively. Results Compared with blank control group, the SOD in brain of experimental control group decreased significantly (P<0.05), and the MDA in brain in experimental control group increased markedly (P<0.05). Compared with that of the experimental control group, the SOD in brain in experimental-therapeutic group were climbing since 7 d later after irradiation, the MDA in brain significantly lower than those experimental control group(P<0.05). Conclusions MgSO₄ used in early stage can inhibit the lipid peroxidation after radiation-induced acute brain injuries and alleviate the damage induced by free radicals to brain tissue.