Brain tissue is highly susceptible to oxidative damage due to its high utilization of oxygen and its poorly developed antioxidative defense mechanisms. Radiation or pro-oxidants interact with cells and tissues through secondary ionization mechanisms such as lipid peroxidation (LPO). LPO can be inhibited by antioxidants such as vitamins A, C, and E and the carotenoid beta-carotene. beta-Carotene, the provitamin A, plays an important radioprotective role due to its properties as a potent free radical scavenger, singlet oxygen quencher, and lipid antioxidant. Amaranthus gangeticus Linn., widely considered as a weed, has a high content of carotene, ascorbic acid, and folate and may prove an efficient antioxidant. To evaluate the antioxidative efficacy of Amaranthus, healthy Swiss albino mice from an inbred colony were treated with alcoholic extract of A. gangeticus leaves (AE) for 2 weeks, at 800 mg/kg body weight, before radiation exposure. Irradiated mice were examined and autopsied at intervals of 1, 3, 7, 15, and 30 days after exposure. Brain was removed by skull dissection, and various biochemical changes were sought. Radiation caused a maximum increase of 27% in LPO and a maximum decrease of 27.96% in protein content at day 7 in controls. However, in the experimental group the increase in LPO was 9.98% and the increase in protein content was 18.78% at day 7. By day 30 after irradiation, AE brought these values to near-normal levels. AE protected brain biochemical activity in this murine study and may prove beneficial for clinical use as a radioprotector.