In this paper, we investigated the primary reduction and oxygen replenishing processes over Mn substitutionally doped CeO₂(111) surfaces by density functional theory with the on-site Coulomb correction (DFT + U). The results indicated that Mn doping could make the surface much more reducible and the adsorbed O₂ could be effectively activated to form superoxo (O₂ ⁻) and/or peroxo species (O₂ ²⁻). The Mn doping induced the Mn 3d–O 2p gap state instead of Ce 4f acting as an electrons acceptor and donor during the first oxygen vacancy formation and O₂ replenishing, which helped to lower the formation energy of the first and second oxygen vacancies to −0.46 eV and 1.40 eV, respectively. In contrast, the formation energy of a single oxygen vacancy in the pure ceria surface was 2.08 eV and only peroxo species were identified as the O₂ molecule adsorbed. Our work provides a theoretical and electronic insight into the catalytic redox processes of Mn doped ceria surfaces, which may help to understand the enhanced catalytic performances of MnO_x–CeO₂ oxides, as reported in previous experimental works.