Mahwangsan is used in the treatment of asthma due to wind and cold(風寒喘). This study was carried out to investigate the effect of Mahwangsan extract and each drug composing it on the contractile force of the isolated guinea pig trachea muscle and elucidate its mechanism. The results were obtained as follows; 1. The isolated trachea smooth muscle of guinea pig was signifi-cantly relaxed by the administration of Mahwangsan extract. 2. The contractile response of the isolated trachea smooth muscle of guinea pig to histamine was significantly inhibited by the administration of Mahwangsan extract. 3. The contractile response of the isolated trachea smooth muscle of guinea pig to histamine was significantly inhibited by the administraction of Herba Ephedrae, Cortex Cinnamoni, Flos Farfarae, Fructus Chebulae and Semen Armeniacae extract. 4. The contractile response of the isolated trachea smooth muscle of guinea pig to acetylcholine was significantly inhibited by the administration of Mahwangsan extract. 5. The contractile response of the isolated trachea smooth muscle of guinea pig to acetylcholine was significantly inhibited by the administration of Herba Ephedrae, Flos Farfarae, Fructus Chebulae and Semen Armeniacae extract. 6. The contractile response of the isolated trachea smooth muscle of guinea pig to 5-hydroxytryptamine was significantly inhibited by the administration of Mahwangsan extract. 7. The contractile response of the isolated trachea smooth muscle of guinea pig to 5-hydroxytryptamine was significantly inhibited by the administration of Herba Ephedrae, Flos Farfarae, Fructus Chebulae and Semen Armeniacae extract.