The influence of the structural characteristics of dispersed Pt electrocatalysts on O-2-electroreduction in acid solution has been studied. Facetted Pt crystallites with preferential crystallographic orientation were grown on carbon substrates by pulsating electrolysis in chloroplatinic acid solution. The dependence of the structural characteristics of the dispersed metal, as revealed by SEM, STM and X-ray diffractometry, on the parameters of the electrical perturbation was determined. O-2-electroreduction steady-state polarization curves for different types of high surface area facetted Pt crystallites in acid solution were obtained. The role of Pt crystallite surface morphology on the O-2-electroreduction reaction in acid electrolyte is examined and results are compared with those obtained on low surface area facetted Pt electrodes.