Effects of the reduction temperature and the pH value of Pt precursor solutions of the polyol reduction process on the resulted Pt electrocatalysts supported on the reduced graphene oxide (Pt/r-GO) nanosheets for the ORR (oxygen reduction reaction) are investigated. The Pt/r-GO catalyst possesses Pt nanoparticles having an average size from 2 to 4 nm and a Pt loading from 13 to 20 wt%. The electrochemical performance of the Pt/r-GO catalysts is examined with the glassy carbon RDE (rotating disk electrode) technique in the O-2-saturated HClO4 (0.5 M) solution. The Pt/r-GO catalysts have less ORR limiting currents near 3.5 mA cm(-2), but, in general, the more positive onset potentials than the commercial Pt/carbon black catalysts. The number of electron transfer in ORR over the Pt/r-GO catalysts is 3.85 in average, close to that of a 4-electron transfer process. (C) 2014 Elsevier Ltd. All rights reserved.