Endothelial dysfunction is the major cause of vascular complications in diabetes. Teucrium polium L. is traditionally used for the production of antidiabetic herbal medicine. The cardiovascular effects of T. polium, has also been reported. As a result of this, the present study was conducted to evaluate the impacts of T. polium hydroalcoholic extract on the vasoreactivity and endothelial nitric oxide synthase (eNOS) and vascular cell adhesion molecule (VCAM)-1 genes expression as well in streptozotocin (STZ)-induced diabetic rat aorta. Male Wistar rats were randomly divided into six groups: control, diabetic, metformin, and three groups of T. polium (TP 100, TP 200, and TP 400). The control and diabetic groups were given normal saline; metformin group was given 300 mg/kg metformin; and T. polium groups were given 100, 200, and 400 mg/kg T. polium extract, daily by gavage for 6 weeks. T. polium extract was found to significantly reduce serum glucose level. It was also observed that metformin and T. polium extract significantly improved vasorelaxant response of aortic rings to acetylcholine (Ach). Real-time polymerase chain reaction (PCR) analysis showed that T. polium and metformin significantly increased eNOS expression, while it decreased VCAM-1 expressions in aortic tissue of diabetic rats. The results showed that T. polium extract could improve endothelial dysfunction by ameliorating the vasoreactivity and regulating eNOS and VCAM-1 gene expressions as well in STZ-induced diabetic rats' aorta.