Oxidative stress is currently hypothesized to be a mechanism underlying diabetes. The present study was designed to evaluate the effect of umbelliferone (UMB), a derivative of coumarin, on erythrocyte lipid peroxidation, antioxidants, and lipid profile in normal and streptozotocin (STZ) diabetic rats. Diabetes was induced in adult male albino rats of Wistar strain, weighing 180 to 200 g, by the administration of STZ (40 mg/kg/b-wt) intraperitonially. The normal and diabetic rats were treated with UMB in 10 percent dimethyl sulfoxide (DMSO) dissolved in water for 45 days. The diabetic rats had elevated levels of blood glucose and lipid peroxidation markers such as thiobarbituric acid reactive substances (TBARS), conjugated dienes (CD), and lipid hydroperoxide (HP) and decreased levels of nonenzymatic antioxidants (Vitamin C and reduced glutathione [GSH]), elevated levels of vitamin E, and elevated levels of enzymatic antioxidants (superoxide dismutase [SOD], catalase [CAT], glutathione peroxidase [GPx]), elevated glucose-6-phosphate dehydrogenase activity, and altered lipid profile (cholesterol and phospholipids) in erythrocytes. These changes were reversed by treatment with UMB. Thus, our results indicate that the administration of UMB shows promising potential for the restoration of normal blood glucose levels, erythrocyte lipid peroxidation, antioxidants, and lipid profile in STZ-diabetic.