The present work examined the effect of oral administration of rutin and its combination with metformin, an antidiabetic drug on blood glucose, total cholesterol and triglycerides level and vascular function in streptozotocin (STZ) -induced diabetic rats. Male Sprague Dawley rats were rendered diabetic by a single intraperitoneal injection of STZ (50 mg/kg). Rutin and metformin were orally administered to diabetic rats at a dose of 100 mg/kg and 300 mg/kg body weight/day, respectively, for 4 weeks. Plasma analysis was conducted to determine changes in the plasma glucose and lipid levels. Rat aortic ring reactivity in response to endothelium-dependent (acetylcholine, ACh) and endothelium-independent (sodium nitroprusside, SNP) relaxants, and to the α1-adrenergic agonist phenylephrine (PE) were recorded. Histology of pancreas, liver and kidney were evaluated. In results, rutin and metformin alone and in combination has led to significant deterioration in blood glucose, cholesterol and triglyceride levels compared to diabetic and normal control. Diabetic aortic rings showed significantly greater contraction in response to PE, and less relaxation in response to ACh and SNP. Treatment with rutin and metformin in combination significantly reduced PE-induced contraction and increased ACh-induced and SNP-induced relaxation in diabetes when compared to rutin or metformin alone. Better histological improvements were recorded with combination treatment. In conclusion, rutin and metformin combination therapy has the most potentiality for restoring blood glucose and lipid level as well as vascular function.