Background:The relaxant and anticholinergic (functional antagonism) effects, histamine H1 inhibitory effect, and calcium channel blocking effect of Nigella sativa have been demonstrated on guinea pig tracheal chains. Several therapeutic effects including anti-asthma and dyspnea have also been ascribed to the seeds of Nigella sativa. Objective: To evaluate the antitussive effect of this plant. Methods: The antitussive effects of aerosols of two different concentrations of aqueous and macerated extracts as well as an extract of concentrated boiled seeds, codeine, and saline were tested by counting the number of coughs produced 10 min after exposing animal to aerosols of different solutions of citric acid (n=7 for each solution). Results: The results showed significant reduction in the number of coughs obtained in the presence of both concentrations of aqueous and macerated extracts, boiled seeds extract and codeine (p<0.05 to p<0.001). The cough number induced in the presence of higher concentrations of aqueous and macerated extracts were also significantly less than those with lower concentrations (p<0.05 for aqueous and p<0.01 for macerated extracts). There was no significant difference between the number of coughs obtained in the presence of all extracts with that of codeine. Conclusion: These results indicate an antitussive effect of Nigella sativa comparable to that of codeine.