Abstract: Carbon supports were modified by different treatments, including gasification under a gas flow of 5%O₂+N₂ in the range of 385-425 ℃ and oxidation with concentrated HNO₃ under controlled conditions, in order to obtain materials with different surface properties. The modified carbon supports were directly impregnated with the aqueous chloroplatinic acid to generate Pt/C catalysts. Analytic results by XRD and TEM demonstrate that the dispersion of platinum crystallites on the modified carbon supports is very high with a mean diameter of 7 nm, while the segregation of platinum crystallites occurs obviously for unmodified carbon supports.