This study was designed to evaluate the protective effect of kolaviron (KV), a biflavonoid from Garcinia kola seeds, against γ-radiation (5 Gy)-induced oxidative stress in brain of Wistar rats. Vitamin C (VC) served as standard antioxidant. Forty-four rats were divided into 4 groups of 11 animals each. One group was un-irradiated (normal), two groups were treated with KV and VC (250 mg/kg) for 6 weeks prior to and 8 weeks after irradiation, and fourth group was only irradiated. Rats were sacrificed 1 and 8 weeks after irradiation. Cellular alterations were monitored using changes in the levels of malondialdehyde (MDA)—an index of lipid peroxidation, superoxide dismutase (SOD), glutathione-S-transferase (GST), reduced glutathione (GSH), catalase (CAT), alanine and aspartate aminotransferases (ALT and AST), urea and creatinine. MDA levels increased significantly (p<0.05) by 90% and 151% after 1 and 8 weeks of irradiation. Furthermore, levels of GSH and antioxidant enzymes were significantly (p<0.05) decreased in γ-irradiated animals. GSH and GST decreased by 61% and 43% after 1 week, and by 75% and 74%, after 8 weeks of exposure, respectively. γ-Irradiation decreased SOD and CAT levels by 53% and 68%, respectively, and caused significant (p<0.05) increases in serum ALT, AST and urea after 8 weeks of exposure. Treatment with KV and VC significantly decreased the levels of MDA, ALT, AST and urea. The antioxidant indices were significantly ameliorated in KV-treated animals. These data suggest that kolaviron may protect against γ-radiation-induced oxidative stress in brain of exposed rats.