Dendrimer-encapsulated Pt nanoparticles (G4OHPt) were prepared by chemical reduction at room temperature. The G4OHPt, with average diameters of ca. 2.7 nm, were characterized by X-ray diffraction, scanning electron microscopy, and thermogravimetric analysis. Electrocatalytic behavior for oxygen reduction reaction was investigated using a rotating disk electrode configuration in an acidic medium, with and without the presence of methanol (0.01, 0.1, and 1 M). Kinetic studies showed that electrodes based on Pt nanoparticles encapsulated inside the dendrimer display a higher selectivity for ORR in the presence of methanol than electrodes based on commercial Pt black catalysts. Also, the dendritic polymer confers a protective effect on the Pt in the presence of methanol, which allows its use as a cathode in a direct methanol fuel cell operating at different temperatures. Good performance was obtained at 90 A degrees C and 2 bar of pressure with a low platinum loading on the electrode surface.