Redox properties of molybdenum in K8[P2W18Mo2CO2(H2O)2O68][MoO6]· 15H2O and its derivatives in which Co atoms were substituted by Fe or Ni were studied with cyclic voltammetry. In addition, it was found that the cobalt-containing compound possesses electrochemical catalysis to the reduction reactions of O2 and NaNO2 to different extents.