Nigella sativa (N. sativa) is a spice plant which has been traditionally used for culinary and medicinal purposes. Different therapeutic properties including the beneficial effects on asthma and dyspnea, digestive and gynecology disorders have been described for the seeds of N. sativa. There is evidence of the relaxant effects of this plant and some of its constituents on different types of smooth muscle including rabbit aorta, rabbit jejunum and trachea. The relaxant effect of N. sativa could be of therapeutic importance such as bronchodilation in asthma, vasodilation in hypertension and therapeutic effect on digestive or urogenital disorders. Therefore in the present article, the relaxant effects of N. sativa and its constituents on smooth muscles and its possible mechanisms as well as clinical application of this effect were reviewed.