The leaf of Psidium guava is traditionally used in Asia to manage, control and treat diabetes. We designed this study to elucidate the effect of the administration of oral doses of aqueous and ethanol extract from Psidium guava leaves on plasma glucose, lipid profiles and the sensitivity of the vascular mesenteric bed to Phenylephrine in diabetic and non diabetic rats. Animals were divided into 5 groups (n = 10): two groups served as non-diabetic controls (NDC), while the other groups had diabetes induced with a single injection of streptozotocin (STZ). Psidium guava-treated chronic diabetic (PSG-CD) and Psidium guava-treated controls (PSG-C) received 1g/l of Psidium guavaadded to the drinking water for 8 weeks. The mesenteric vascular beds were prepared using the McGregor method. Administration of Psidium guava caused Ca/Mg ratio, plasma glucose, high density lipoprotein (HDL), low density lipoprotein (LDL), very low density lipoprotein (VLDL), total cholesterol and triglyceride concentrations to return to normal levels, and was shown to decrease alteration in vascular reactivity to vasoconstrictor agents. Our results support the hypothesis that Psidium guava could play a role in the management of diabetes and the prevention of vascular complications in STZ-induced diabetic rats