Antimuscarinic agent like antispasmodic actions of licorice alkaloidal fraction, obtained from the Glycyrrhiza glabra L., was compared with that of atropine quantitatively. For this purpose, the author calculated the kinetic constants and ED₅₀ for acetylcholine antagonism by these drugs on rat ileum and guinea-fig ileum longitudinal muscle according to Paton s theoretical equations describing the combination of an antagonist drug with its receptors. The results are as follows. 1. On rat ileum. a) Licorice alkaloidal fraction K₁ (association rate constant)=4.078×10²(s^-1 gm^-1 ml) K₂ (dissociation rate constant)=6.986×10^-4 (s^-1) ED₅₀ K₂/K₁)=1.772×10^-6(gm/ml) b) Atropine K₁=5.136×10⁶, K₂=7.714×10^-4, ED₅₀=1.408×10^-10 2. On guinea-pig ileum longitudinal muscle a) Licorice alkaloidal fraction K₁=1.30×10², K₂=1.25×10^-3 ED₅₀=9.58×10^-6 b) Atropine K₁=5.75×10⁶, K₂=1.54×10^-3 ED₅₀=2.68×10^-10 Above results present that 1 r of licorice alkaloidal fraction has equal fotency of acetylcholine antagonism with 8.5×10^-5r of atropine on rat ileum, 2.8×10^-5r on guinea-pig ileum longitudinal muscle. This facts suggest that the site and numbers of licorice alkaloid receptors of guinea-pig ileum are different from that of rat ileum. Besides, it also gives a suggestion that licorice alkaloidal fraction may be a partial antagonist on guinea-pig ileum in this e×perimental conditions.