Oxidative stress plays an important role in chronic complications of diabetes mellitus. In the current study, the antioxidant effect of oral administration of aqueous bark extract of Garuga pinnata Roxb. (Burseraceae) on tissue antioxidant enzymes and lipid peroxidation in liver and kidney of streptozotocin-nicotinamide-induced type II diabetic rats was evaluated. The diabetic rats showed lower activities of superoxide dismutase (SOD), glutathione peroxidase, glutathione transferase, and reduced glutathione content in liver and kidney, which were restored to near normal levels by treatment with the bark extract. The increased levels of lipid peroxidation (TBARS) in diabetic rats were reverted back to near normal levels after treatment with the bark extract. A two dose level study was conducted. The current study reveals the efficacy of Garuga pinnata aqueous bark extract in the amelioration of diabetes, which may be attributed to its antioxidant potential. © 2007 Informa Healthcare.