The oxygen reduction activities of sputter-deposited platinum (Pt) thin films of various thicknesses on amorphous carbon (a-C), tungsten oxide (WO3), and titanium oxide (TiO2) were examined to investigate the effect of the support materials. An X-ray diffraction analysis showed that the Pt lattice constant clearly increased with decreasing Pt thickness on the a-C, while it did not change on the WO3 and TiO2. The oxygen reduction activity of the catalysts was measured electrochemically in 0.5 mol/L sulfuric acid at 308 K. The measurements showed that the activity of Pt/a-C catalysts decreased with the Pt thickness. However, decrease of activity was not observed in the Pt/WO3 and Pt/TiO2 catalysts. The correlation between catalytic activity and Pt lattice strain was obtained from these results; Pt lattice expansion, which was observed on the a-C support, resulted in the decrease of catalytic activity for an oxygen reduction reaction. The metal-oxide support, such as the WO3 and TiO2, suppresses the Pt lattice expansion and maintains the Pt catalytic activity in the case of decreasing Pt thickness compared to the a-C support. (C) 2012 Elsevier B.V. All rights reserved.