Abstract: The optimum conditions for the co-coloration effect of theco-colored heteropolynuclear coordination compounds in the system of "Alkaline earths(Ⅱ)-Rare earths(Ⅲ).Alizarin violet-Tetradecylpy ridinium chloride" are reported. By analysis of the experimental results, it comes to the following conclusions; the radius of ion or ratios of radii, but not the hyclrolytic properties of the metal ions, play an important role in the co-coloralion of the heteropolynuclear coordination compounds. There is a possibility to search for a new co-coloration system, though different system has different optimum ratio of the radii.