The oxygen reduction reaction (orr) was studied on composite electrodes GC/PPy/PPy(Ni x Co3−x O4)/PPy with x=0.3 and 1, in 2.5×10−3 M KOH+0.8 M KCl at room temperature. The orr takes place on the oxide particles with formation of hydrogen peroxide (H2O2), which diffuses through the polymer layers to reach the bulk of electrolyte solution. The amount of H2O2 produced, determined indirectly by iodine spectrometry, depended strongly on the oxide stoichiometry. The effects of the orr and of the generation of H2O2 on the conductivity of PPy and on the behaviour of the embedded oxide particles are discussed.