Precipitation reaction was found to occur when each 5×10^-4 M aqueous solution of berberine (I) and glycyrrhizin (II) were blended. The molar ratio of I and II in the precipitate (III) was revealed to be 2 : 1 by observation of UV absorption at 251 and 350 nm. By comparison of the IR absorption near at 1715 and 1620 cm^-1 of II, III, soyasaponin III and glycyrrhetinic acid after treated at various pH, it was revealed that the quartery base moiety of I bound on the glucouronic acid moieties of II ionically in compound III. The solubility of III in aqueous solution was 0.09% at pH 3.5, while it increased up to 1.9% at pH 6.8. The solubility of III was slightly decreased by addition of II in aqueous solution.