Objective: To determine the anti-asthmatic activity of Argemone mexicana ethanolic extract and its chloroform and ethyl acetate fractions. Methods: Present study was designed to evaluate the anti-asthmatic activity of Argemone mexicana stems using various experimental in vivo and in vitro animal models. Ethanolic extract of Argemone mexicana and its chloroform and ethyl acetate fractions were evaluated for its anti-asthmatic activity by in vitro models (isolated guinea pig ileum preparation and isolated guinea pig tracheal chain preparation) in vivo models (Histamine and acetylcholine induced bronchospasm in guinea pigs and milk induced eosinophilia in mice models). Results: Ethanolic extract of Argemone mexicana significantly antagonized the effect of histamine induced contraction on isolated guinea pig ileum preparation. Ethanolic extract of Argemone mexicana, and its ethyl acetate fraction at the concentration of 10mg significantly inhibited the contraction of isolated guinea pig ileum and trachea chain preparation produced by histamine. Ethanolic extracts of Argemone mexicana at dose of 150, 250, and 350mg/kg body weight significantly extended the latent period of convulsion as compared to standard (Ketotifen fumarate) upon histamine and acetylcholine exposure in a dose dependent manner. Conclusion: Ethanolic extract of Argemone mexicana stems have shown significant anti-asthmatic activity.