These studies were carried out to investigate the effect of Mahwangchangchultang water extract on the inhibitory contractile action of acetylcholine in guinea pig. The results of these studies were as follows; 1. Contractile force of acetylcholine from trachea smooth muscle in guinea pig was significantly inhibited by Mahwangchangchultang 2. Dose-response of acetylcholine pretreated Mahwangchangchultang in guinea pig was not significantly changed. 3. Inhibitory contractile action of acetylcholine pretreated propranolol in guinea pig was decreased. 4. Inhibitory contractile action of acetylcholine pretreated indomethacin was not significantly changed by Mahwangchangchultang. 5. Inhibitory contractile action of acetylcholine pretreated methylene blue was not significantly changed by Mahwangchangchultang.