Rare-earth-element (Y, Gd) modified Pt nanoparticles (NPs) supported on a carbon substrate (Vulcan XC-72) are synthesized via a water-in-oil chemical route. In both cases, X-ray diffraction (XRD) measurements show the non-formation of an alloyed material. Photoemission spectroscopy (XPS) results reveal that Y and Gd are oxidized. Additionally, no evidence of an electronic modification of Pt can be brought to light. Transmission electron microscopy (TEM) studies indicate that Pt-Y2O3 and Pt-Gd2O3 particles are well dispersed on the substrate—and that their average particle sizes are smaller than the Pt-NP sizes. The catalytic activity of the Pt-Y2O3/C and Pt-Gd2O3/C catalysts towards the oxygen reduction reaction (ORR) is studied in a 0.5 M H2SO4 electrolyte. The surface and mass specific activities of the Pt-Y2O3/C catalyst towards the ORR at 0.9 V (vs. the reversible hydrogen electrode, RHE) are (54.3±1.2) μA cm−2Pt and MA=(23.1±0.5) mA mg−1Pt, respectively. These values are 1.3-, and 1.6-fold higher than the values obtained with a Pt/C catalyst. Although the as-prepared Pt-Gd2O3/C catalyst has a lower catalytic activity for the ORR compared to Pt/C, the heat-treated sample shows a surface specific activity of about (53.0±0.7) μA cm−2Pt, and a mass specific activity (MA) of about (18.2±0.5) mA mg−1Pt at 0.9 V (vs. RHE). The enhancement of the ORR kinetics on the Pt-Y2O3/C and heat-treated Pt-Gd2O3/C catalysts could be associated with the formation of platinum NPs presenting modified surface properties.