Abstract: By using radioligand binding assay method, the effects of n-butyl-scopolamine and scopolamine on the M-cholinergic receptors of rat brain and longitudinal muscle of guinea pig ileum were compared. The results showed that the affinities of n-butyl-scopolamine for central and peripheral M-receptors were lower than those of scopolamine. Both drugs, however, didn't show any effect on the GABA receptor of rat brain. The intrinsic activity of both drugs for M-receptor on isolated guinea pig ileum were also determined. Scopolamine and n-butyl-scopolamine, at concentrations of 10^-6mol/L and 10^-7～10^-8mol/L respectively, shifted the cumulative dose-response curve of Ach to the right, indicating that there is a correlation between the biological activity and the affinity for M-receptor. The two drugs were also shown to impair acquisition of memory in one trial passive avoidence responses in mice, but the efficacy of n-butyl-scopolamine was 10-20 times lower than that of scopolamine.