A series of CeO2-MnOx composite oxides were synthesized through hydrothermal method and the complete catalytic oxidation of benzene were examined. The effects of the Ce-at/Mn-at atomic ratio on the features of catalyst structure and catalytic behavior were researched. The results exhibited that the catalytic properties of CeO2-MnOx composite oxides were higher than pure CeO2 or MnOx. When the Ceat/Mnat ratio was 3:7, the catalytic activity reached the best. By means of testing, the data revealed that the synergistic effects existed in the composite oxides, which resulted in the enhancement of catalytic abilities. In the main phase, MnOx provided available oxygen species and CeO2 enhanced oxygen mobility. In addition, the nature of oxygen vacancy of catalysts was also studied through positron annihilation spectrum. The results showed that the concentration of oxygen vacancy for CeO2-MnOx composite oxides changed comparing with pure CeO2 or MnOx, which also caused the activity differences over benzene. (C) 2013 Elsevier B.V. All rights reserved.