Platinum colloidal nanoparticles were synthesized by chemical reduction of metallic salts in presence of poly (N-vinyl-2-pirrolidone) which served as a protecting agent. The preparation conditions for obtaining Pt nanoparticles were established by analyzing TEM and HRTEM images of the samples. Size of the synthesized Pt nanoparticles was in the range 2.5 to 8.5 nm depending on the molarity of PtCl(4) used to prepare the colloidal dispersion. The electrochemical characteristics of the Pt nanoparticles supported on carbon were investigated by analyzing their catalytic response to the oxygen reduction reaction (ORR). The reactivity of the prepared catalyst was comparable to that of the commercially available carbon supported Pt for the ORR. Catalytic parameters like charge transfer coefficient, Tafel constants and exchange current density were calculated for the prepared catalyst. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.