Gold nanoparticles sputter-deposited in ionic liquids were densely immobilized on the surface of highly ordered pyrolytic araphite (HOPG) by spreading the ionic liquid containing An nanoparticles on HOPG and then heating. The density of immobilized ALL particles was greatly dependent on the kind of ionic liquid used, and their size was controlled by the heating temperature. The resulting nanoparticle films were stable and electrochemically active for oxygen reduction.