Cubic perovskite SmxSr1-xMnO3 (SSM) surface and bulk models have been constructed to simulate the oxygen reduction reactions by employing first-principles calculations. The results demonstrate that oxygen vacancies can be formed easily in Sm0.5Sr0.5MnO3 (SSM50). The oxygen migration barrier in bulk SSM50, which is predicted by the nudged elastic band (NEB) method, is the lowest, while the adsorption energy of O-2 molecular on SSM50 (100) surface is the lowest among the considered doping systems, indicating the potential application of SSM50 as a cathode for intermediate-temperature solid oxide fuel cell (IT-SOFC). The reaction mechanisms of oxygen reduction on SSM50 (100) surface have also been studied. (C) 2013 Elsevier B.V. All rights reserved.