A new tertiary phenolic base, thalicberine, was isolated from the leaf base of Thalictrum Thunbergii DC, as colorless needles of m. p. 161°(sint. 155°), [α]D+231.2° (CHCl3), and a new tertiary non-phenolic base, O-methylthalicberine, as colorless needles, m. p. 186~187°, [α]D+265.9°(CHCl3). This latter base was also isolated from the leaf base of commercial crude drug, "Takatogusa". On the other hand, thalicberine was O-methylated to form O-methylthalicberine and this was proved to be identical with natural O-methylthalicberine from elementary analytical values, optical rotation, mixed fusion, and by comparison of infrared spectra in Nujol. The composition and empirical formula of thalicberine are represented as C37H40O6N2·H2O = C32H24O2(OCH3)3(OH)(N-CH3)2·H2O, and those of O-methylthalicberine as C38H42O6N2 = C32H24O2(OCH3)4(N-CH3)2. O-Methylthalicberine dimethochloride was submitted to the Hofmann degradation to be derived to the methylmethine which was oxidized with potassium permanganate to form 2-methoxydiphenyl ether-5,4'-dicarboxylic acid (I). The experimental evidences, ultraviolet spectra (Fig. 1, A and B), and optical rotation suggest that both these are new bases closely related to the oxyacanthine-berbamine series of the biscoclaurine-type bases.