Platinum nanoparticles supported on acid-treated multi-walled carbon nanotubes (Pt/MWCNT) catalysts were prepared through magnetron sputtering of Pt. The prepared Pt/MWCNT composites were annealed at different temperatures to study heat-treatment effects on the particle size, surface morphology, and the oxygen reduction reaction (ORR) activity. High-resolution scanning electron microscopy (SEM) was used to study the surface morphology of Pt/MWCNT catalysts. For surface characterization, CO oxidation and cyclic voltammetry were performed in 0.1 M KOH and 0.05 M H2SO4 solutions. The ORR activity of the electrocatalysts annealed at different temperature was studied in these solutions using the rotating disk electrode (RDE) method and the results were compared to those of the commercial Pt/C catalysts. Specific activity for oxygen reduction on Pt/MWCNT catalysts was higher than that of Pt/C, however, the mass activity was lower due to a larger Pt particle size of Pt/MWCNT catalysts. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.