The electrocatalytic properties of gold nanoparticles covalently capped with a monolayer film of 1,4-decylphenyl groups for oxygen reduction in an alkaline solution have been studied Functionalized nanoparticles were adsorbed on a film of the same capping ligand previously grafted to a glassy carbon electrode The molecular film-nanoparticle assembly was characterized by cyclic voltammetry and XPS It is shown that although the at of the capping ligand to the electrode surface blocks direct electron transfer, the metal centers of the incorporated nanoparticles provide sites for electron tunneling from the electrode surface thus leading to sites where oxygen reduction can take place Rotating disk voltammetry shows that the oxygen reduction reaction follows mainly a peroxide formation channel on these nanostructured surfaces The capping ligand greatly influences the reduction mechanism by establishing a local hydrophobic environment at the reaction centers within the film.