Introduction: Several reports have shown the various medicinal effects of grape (Vitis vinifera) seed and skin extracts, such as antioxidant, hypotensive and vasodilatory effects. It has been recently shown the relaxatory effect of grape leaf hydroalcoholic extract on rat ileum, uterus, aorta, trachea and vas deferens as well as on frog isolated heart. The aim of the present study was to investigate the effect of Vitis vinifera leaf hydroalcoholic extract (VLHE) on contractility of urinary bladder smooth muscle in male rats and to study the mechanism(s) of its action. Materials and Methods: The extract of dried grape leaf was prepared by macerated method using 70% ethanol for 72h in room temperature. The solvent was then evaporated. Urinary bladder was removed from male adult wistar rats after induction of deep anaesthetize by di-ethyle-ether. Tissues were then suspended in the organ bath containing physiologic solution (37^oC, pH 7.4) bubbled with oxygen. Contractions were recorded isometrically under 1g resting tension. Results: VLHE at 1, 2, 4 and 8 mg/ml significantly reduced the urinary bladder contractions evoked by KCl (60 mM P<0.05) and (0.5, 1, 2 and 4 mg/ml) also reduced the contractions evoked by Acetylcholine (5 µM) dose dependently (P<0.05). In calcium free physiologic solution, KCl-induced (120 mM P<0.05) contractions were occurred only after adding calcium (0.312, 0.625, 1.25, 2.5 and 5 mM) to the organ bath solution. VLHE (2 mg/ml) also reduced different concentration of calcium-induced contraction in the presence of KCl (P<0.05). The VLHE- induced urinary bladder relaxation was unaffected by propranolol (1 µM for 20 mins) while the presence of tetraethylamonium (10 mM for 20 mins) could strongly reduce the relaxatory effect of VLHE. Conclusion: The data suggest that VLHE induces spasmolytic effect in rat urinary bladder, possibly via blocking voltage dependent calcium channels and activation of calcium-activated potassium channels.