These studies were carried out to investigate the effects of Macmundongtang extract on the inhibitory contractile action of acetylcholine in control rat. The results of these studies were as follows: 1. Contractile force of acetylcholine from tracheal smooth muscle in control rat was significantly inhibited by Macmundongtang. 2. Inhibition contractile action of acetylcholine pretreated ACH $ED_{50}$ in control rat was significantly changed. 3. Dose-response of acetylcholine pretreated Macmundongtang in control rat was not significant. 4. Inhibitory contractile action of acetylcholine pretreated propranolol in control rat was not significantly changed by Macmundongtang. 5. Inhibitory contractile action of acetylcholine pretreated methylene blue in control rat was significantly changed. 6. Contractile force of acetylcholine pretreated indomethacin from trachea smooth muscle in control rat was not significantly inhibited by Macmundongtang.