The simultaneous anodic oxidation of Pb2+ and Co2+ in a sulphamate bath containing suspended Co3O4 (or NiCo2O4) particles has been studied as a method for preparing composite oxides in which the particles are dispersed in a matrix consisting of PbO2 and hydrous Co oxides, CoO x with x<2. The (PbO2+CoO x )+Co3O4 composites thus prepared are very rough and their Co concentration, expressed as X Co=N Co/(N Co+N Pb), where N represents the number of atoms, approaches 0.5. As a result, they are more active catalysts in the oxygen evolution reaction than either PbO2+CoO x or PbO2+Co3O4 prepared in the past by our group. For samples prepared in the presence of particles, the potential required to evolve oxygen at a fixed current density varies roughly linearly with X Co, irrespective of the fact that Co is present as Co3O4 or CoO x .