The present study was designed to examine the antioxidative potential and antihyperlipidemic activity of Swietenia macrophylla in streptozotocin diabetic rats. The experimental groups were rendered diabetic by intraperitoneal injection of a single dose of streptozotocin (STZ; 40 mg/kg body weight, BW). Rats with glucose levels >200 mg/dL were considered diabetic and were divided into five groups. Three groups of diabetic animals were orally administered daily with seed extract (SME) at a dosage of 50, 100 and 200 mg/kg BW. One group of STZ rats was treated as diabetic control and another group orally administered 600 μg/kg BW glibenclamide daily. Repeated daily oral administration of S. macrophylla significantly reduced blood glucose levels after 45 days of treatment. The lipid peroxidation products such as thiobarbituric acid reactive substances and lipid hydroperoxides of SME treated rats decreased in the plasma, liver and kidney. Glutathione peroxidase, superoxide dismutase and catalase activity were significantly increased in SME treated rats. Antioxidants such as reduced glutathione level in the plasma, liver and kidney and vitamins C and E levels in the plasma increased in SME treated rats. Total cholesterol, triglycerides, phospholipids and free fatty acids and lipoproteins levels increased. Altered lipid profile of treated rats lead to normality with treatment of S. macrophylla. Thus, our results indicate that the administration of 100 mg/kg BW SME restores near normal blood glucose, redox status and lipid profile in STZ-diabetic rats.