The electrochemical behavior of lanthanide elements deposited on liquid zinc cathodes was studied using cyclic voltammetry (CV) and open circuit chronopotentiometry (OCP). We observed abimodal effectin the equilib-rium deposition potentials of zinc with lanthanides. A mathematic equation is derived to illustrate the relation-ship between the equilibrium potential of the intermetallic compounds formed by lanthanide elements and zinc and their atomic radius. This equation is not only applicable to lanthanide elements but also hold for other elements such as alkali metal lithium, alkaline earth metal magnesium, calcium and transition metal niobium, which have crucial theoretical significance for the electrolysis of intermetallic compounds, the separation, and extraction of metals.