 C–MnO2 is an alternative catalyst support in polymer electrolyte membrane fuel cells. In this study, C–MnO2 was prepared by hydrothermal method using KMnO4 as the Mn source. Meanwhile, Pt/C–MnO2 electrocatalyst was prepared by impregnation chemical reduction using ethylene glycol as reducing agent and H2PtCl6 as Pt precursor. The structure and morphology of C–MnO2 and Pt/C–MnO2 were characterized by X-ray diffraction energy-dispersive spectroscopy and transmission electronic microscopy analyses. Electrochemical performance was investigated by cyclic voltammetry analyses. A rotating disk electrode (RDE) was used to examine catalytic oxygen reduction reactions (ORRs) to explore the oxygen reduction of Pt/C–MnO2. The Pt/C–MnO2 exhibited better activity and stability than those of Pt/C. In contrast to Pt/C, MnO2 possessed unique characteristics; the oxide functions as an effective Pt support and hence enhances ORR activity and durability. The RDE results for the ORR indicated that the main reaction of the Pt/C–MnO2 catalyst was the direct reduction of O2–H2O. This reaction is similar to the mechanism of the Pt/C catalyst and both with a four-electron charge transfer. The results of the single cell polarization experiment and the ON–OFF cycling test revealed that MnO2 improves proton exchange membrane fuel cells performance and durability. This paper also investigated the mechanism through which MnO2 promotes oxygen reduction.