These studies were carried out to investigate the effect of Onpaetang water extract on the inhibitory contractile action of acetylcholine in sensitized rat. The results of these studies were as follows; 1. Contractile force of acetylcholine from trachea smooth muscle in sensitized rat was significantly inhibited by Onpaetang. 2. Dose-response of acetylcholine pretreated Onpaetang in sensitized rat was not significantly changed. 3. Inhibitory contractile action of acetylcholine pretreated propranolol in sensitized rat was decreased. 4. Inhibitory contractile action of acetylcholine pretreated indomethacin was not significantly changed by Onpaetang. 5. Inhibitory contractile action of acetylcholine pretreated methylene blue was not significantly changed by Onpaetang. 6. Inhibitory contractile action of acetylcholine pretreated tetrodotoxin was not significantly changed by Onpaetang.