The direct interaction of metal ion in active center of copper-zinc superoxide dismutase (Cu2Zn2SOD) with inorganic cobalt chloride (CoCl2) in buffer has been first studied by visible spectroscopy. The effects of increasing amounts of CoCl2, changing pH,different acid salt and equilibrium time on the interaction have been discussed. It was found that the Co(II) of CoCl2 makes an exchanging interaction with Zn(II) in Cu2Zn2SOD and thus the partial Cu2Co2SOD is formed.