The purpose of the present study was to investigate whether polyphenol-rich fraction extracted from fruit wine of Rubus coreanum M (PCRC) can affect the contractility of the thoacic aortic strips isolated from spontaneously hypertensive rats (SHRs), and to clarify its mechanism of action. PCRC (200-800 ${mu}g/mL$) concentration-depenedently blocked phenylephrine (10 ${mu}M$)-induced contractile responses of the isolated aortic strips of SHRs. PCRC (400 ${mu}g/mL$), added in to bath medium, also depressed the contractile active tension evoked by both phenylephrine (3 and 10 ${mu}M$) and high potassium (25 and 56 mM). In the simultaneous presence of PCRC (400 ${mu}g/mL$) and L-NAME (a selective inhibitor of NO synthase, 300 ${mu}M$), the contractile responses evoked by phenylephrine and high $K^+$ were recovered to considerable level of the corresponding control contractility compared with those effects of PCRC-treatment alone. However, in the simultaneous presence of indomethacin (10 ${mu}M$, a selective cyclooxygenase inhibitor) and PCRC (400 ${mu}g/mL$), they were not affected. In the endothelium-denuded aortic strips by CHAPS-treatment, PCRC did not affect the contractile responses induced by phenylephrine or high potassium. Interestingly, PCRC (1.0, 3.0 and 10.0 mg/kg/30 min, i.v., respectively) dose-dependently suppressed norepiphrine-induced vasopressor responses in anesthetized SHRs. Collectively, we concluded that PCRC causes vasorelaxation in the thoracic aortic strips with intact endothelium of SHRs at least partly by the increased NO production through the activation of NO synthase of vascular endothelium, but not through the activation of cyclooxygenase. These results suggest that PCRC might be helpful to prevent or alleviate cardiovascular diseases, including hypertension.