In this work, POXC, a laccase from Pleurotus ostreatus, was immobilized on carbon nanotubes (CNTs) modified by electrografting anthraquinone and naphthoate diazonium salts. Thanks to a favorable interaction between laccase and covalently modified CNTs, this laccase exhibits high‐potential/high‐current oxygen reduction reaction (ORR) performances, surpassing the performances of the well‐known laccase from Trametes versicolor (TvLAC) immobilized on the same nanostructured electrodes. Furthermore, immobilized POXC demonstrates high ORR activity over a wide range of pH (2 to 8), being also highly active at a gas‐diffusion electrode. Finally, owing to these unique performances, this enzyme was able to operate at the interface of the microporous layer, humidified air and a polymer electrolyte, that is, Nafion®, in a conventional H2/air proton‐exchange membrane fuel.