An attempt has been made to evaluate the presence of antioxidant properties in the oil of marjoram (Organium majorana L.) in streptozotocin-induced diabetes in rats. Oral administration of marjoram oil at a dose of 100 mg/kg body weight to diabetic rats significantly decreased levels of blood glucose and improved body weights. The increased levels of lipid peroxidation in tissues of diabetic rats were reverted near back to normal levels after the treatment with marjoram oil. The marjoram treatment also resulted in a significant increase in superoxide dismutase, catalase and glutathione peroxidase in the liver and kidney of diabetic rats. These results clearly show the antioxidant properties of marjoram oil. The herbal medicine was also more effective than glibenclamide (standard antidiabetic drug) in restoring values of these parameters.