Co(Ⅱ)-phenanthroline-water ternary complex was synthesized and characterized by elementary analysis and IR. Cyclic voltammetry was used to study the electrochemical behaviour of ligands, Co(Ⅱ) ion, its binary or ternary complexes. In the scan range of -1.0V to +1.0V(vs·SCE) and the ternary complex depicted reversible electron transfer process.