The oxygen reduction reaction (ORR) was studied in KOH electrolyte on different manganese oxides, dispersed on a carbon powder (MnO x /C). The oxides were prepared by different methods, for producing MnO, Mn3O4 and MnO2 as major phases dispersed on the Vulcan XC-72 carbon. The oxides were characterized by XRD (X-ray diffraction) and in situ XANES (X-ray absorption near edge structure). The electrochemical measurements were made using cyclic voltammetry and steady state polarization curves carried out in an ultra-thin layer rotating ring/disk electrode. The results have shown lower activity for the ORR on the MnO x /C species compared to that on Pt/C, but higher activity compared to that of pure Vulcan carbon. Formation of HO 2 - involving 2e− per O2 molecule is the main path of the ORR in the studied MnO x /C catalysts but, at low overpotentials and rotation rates the number of electrons is raised to 4 due to the occurrence of a HO 2 - disproportionation reaction. Large differences of electrocatalytic activity were seen for the different oxide species, and these were related to the presence of a Mn(IV) phase and the occurrence of a mediation processes involving the reduction of Mn(IV) to Mn(III), followed by the electron transfer of Mn(III) to oxygen.