Many reports have shown the various effects of grape (Vitis vinifera L.) seed extract for example antioxidant, protecting RBC against UV, also hypotensive, hypolidemic and vasodilatory effects. We have recently shown the relaxatory effect of grape leaf extract on rat ileum and uterus and frog isolated geart rate and contractility. The aim of present study was to investigate the relaxant effect of vitis vinifera leaf hydroalcoholic extract (VLHE) on isolated rat thoracic aorta contractions induced byphenylephrine and KCI, and the role of aorta endothelium on this action. Rat aorta was removed and placed in an organ bath containing Krebs-Henseleit solution and aorta contractions were recorded isometrically. The results demonstrate that VLHE at 0.125, 0.25, 0.5, 1 and 2 mg/ml reduces the endothelial intact aorta contracted by phenylephrine (1m#M) significantly and dose-dependently. Endothelial denuded aorta slowed the same relaxation but in much less extent. The IC__50 of these two groups were 0.454 ±0.08 and 1.73±0.23 mg/ml respectively. VLHE also reduced the aorta contractions induced by KCI (80mM). The relaxatory effect of VHLE on KCI-induced contractions were less than those evoded by phenylephrine. Soluble guanylate cyclase inhibitor (methylene blue, 10m#M) and nitric oxide synthase ingibitor (L-NAME, 100m#M) reduced the VHLE-induced relaxation in the intact aorta significantly but, atropine (1µM) was unable to decrease this vasorelaxant effect. These results suggest than the most vasorelaxant effect of VHLE on rat aorta is endothelium-dependent and also nitric oxide (NO) and cGMP are involved in this action.