The electrochemical reduction of oxygen on thin-film platinum electrodes in 0.1M HClO4 and 0.05M H2SO4 solutions has been investigated using the rotating disk electrode (RDE) method. Thin films of Pt (0.25-20nm thick) were prepared by vacuum evaporation onto glassy carbon substrate. The surface morphology of Pt films was examined by transmission electron microscopy (TEM). The specific activity of 02 reduction was higher in HClO4 and decreased with decreasing film thickness. In H2SO4, the specific activity was lower and appeared to be independent of the Pt loading. The values of Tafel slopes close to -120mVdec(-1) in high current density range and -60mVdec(-1) in low current density range were obtained for all electrodes in both solutions, indicating that the mechanism Of O-2 reduction is the same for thin-film electrodes as for bulk Pt. The number of electrons transferred per O-2 molecule was close to four for all thin Pt films studied. (C) 2008 Elsevier Ltd. All rights reserved.