Objective: In this study, we investigated the possible effect of ∆ 9 -tetrahydrocannabinol (THC), a peroxisome proliferator-activated receptor gamma (PPARγ) agonist, on metabolic control and vascular complications of diabetes in streptozotocin/nicotinamide (STZ/NIC) induced type 2 diabetes mellitus. Material and methods: Type 2 diabetes was induced with 65 mg/kg STZ, 15 minute later 85 mg/kg NIC was given intraperitoneally (i.p.) to rats. Three days after diabetes induction, THC (3 mg/kg/day, i.p.) was given for 7 days to diabetic rats. Body weight and plasma glucose levels of rats were measured in all groups before and at the end of 3 weeks after diabetes induction. Acetylcholine (Ach) and sodium nitroprusside (SNP) potency and maximum relaxant effects were calculated on aortic rings pre-contracted with noradrenaline (NA). Results: At the end of 3 weeks, blood glucose levels of diabetic group significantly increased in comparison with the control group. Increased plasma glucose levels were significantly decreased by the treatment of THC. Ach induced relaxation was impaired whereas endotheliumindependent relaxation to SNP was unaffected on isolated diabetic rat aorta. THC treatment enhanced Ach induced relaxation on diabetic rat aortas. Discussion: These results suggested that THC improved endothelium-dependent relaxation in STZ/NIC induced diabetic rat aorta and that these effects were mediated at least in part, by control of hyperglycemia and enhanced endothelial nitric oxide bioavailability.Keywords: rat, aorta, ∆ 9 -tetrahydrocannabinol, type 2 diabetes mellitus, STZ/NIC induced diabetes, endothelial dysfunction Type 2 diabetes mellitus comprises an array of dysfunctions resulting from the combination of resistance to insulin and inadequate insulin secretion. These disorders are characterized by hyperglycemia and associated with microvascular and macrovascular complications. In both diabetic patients and animal models, endothelial dysfunction is asserted to have a key role in the progression of macro-and microangiopathy (5, 33).The most psychoactive substance in cannabis is ∆ 9 -tetrahydrocannabinol (THC) and its derivatives have recently taken interest for researchers because of the possible therapeutic use in diabetes. Although the evidence regarding the effects of cannabis on diabetes is complex, ranging from anecdotal reports on benefits and harms to experimental research on