The aim of this study was to evaluate the protective effects of D-limonene on the levels of lipid peroxidation by-products and antioxidant defence systems in the plasma and tissues of normal and streptozotocin (STZ)-induced diabetes rats. The experimental diabetes was induced in rats by a single dose of STZ (40 mg/kg i.p.) injection, and treatment with D-limonene was continued for 45 days. After the treatment period, oxidative stress parameters such as lipid peroxidation by-products; enzymatic antioxidants such as superoxide dismutase, catalase, glutathione peroxidase and glutathione-S-transferase; non-enzymic antioxidants including reduced glutathione, Vitamins C and E were measured in the plasma and tissues of experimental rats. An increase in the levels of lipid peroxidation by-products and significant decrease in antioxidant enzymes were observed in untreated diabetic rats. Administration of D-limonene to diabetic rats for 45 days caused a significant reduction in the levels of lipid peroxidation by-products and an increase in the activities of antioxidant enzymes, when compared with the untreated diabetic group. There was no significant difference in normal treated groups, when compared with normal rats. Biochemical observations were substantiated with the help of histopathological examinations through its antioxidant properties and thereby conferred protection against STZ-induced diabetic rats. The result of this study indicates that D-limonene has antioxidant potential in addition to its antidiabetic effect in experimental diabetes.