Diabetes mellitus and hypertension are a global health problem due to its serious complications, along with oxidative stress were shown to contribute to endothelial dysfunction. The aim of the present study was to investigate the role of beneficial effect of Lcarnitine in healthy and streptozotocin (STZ) Nω-nitro-L-arginine methyl ester (L-NAME) induced diabetes mellitus and hypertension in rats. Results showed that diabetic hypertensive (DH) rats had significant increase in the level of plasma glucose, malondialdhyde (MAD), cholesterol (CH), triglycerides (TG), urea, creatinine, and the activity of serum liver enzymes (AST, ALT) as to normal control rats. While, blood glutathione (GSH) content and erythrocyte superoxide dismutase (SOD) activity and nitric oxide level (NO), were significantly lowered. Supplementation of L- carnitine for 6 weeks improve plasma glucose, lipids, liver and kidney functions, In addition, both normal healthy rats and DH rats treated with L- carnitine showed increase in blood GSH and SOD activity and serum nitrate level (stable product of nitric oxide NO) as compared with healthy control and DH respectively. Histopathological and immunochemical study of heart confirm the biochemical results. It was concluded that administration of L-carnitine reduces or delays oxidative stress in diabetic hypertensive rats.