A series of Ce-La-O mixed oxide catalysts with different compositions have been prepared by sol-gel method and characterized by XRD, BET, Raman, TPR and CO(2)-TPD techniques. The activity of Ce-La-O catalysts for methane oxidation has been investigated. When the ratio of Ce/Ce + La is changed from 1.0 to 0.2, only cubic phase CeO(2) with fluorite structure is observed, whose crystal size decreases significantly with the increase in La amount, due to the formation of LaCeO(x) solid solution. The peak at 533 degrees C on TPR profiles of Ce-La-O with fluorite structure is ascribed to the reduction of non-stoichiometric CeO(2-x). Raman bands around 570 and 1167 cm(-1) for samples with the Ce/Ce + La ratios of 1-0.2 might be assigned to oxygen vacancies and surface superoxide ions, respectively. The addition of La promotes the formation of non-stoichiometric CeO(2-x), which is responsible for the oxygen vacancies and surface superoxide ions. However, when the ratio of Ce/Ce + La decreases to 0.2, ceria-in-lanthanum solid solutions are formed, where non-stoichiometric CeO(2-x) cannot be observed. The high activity of Ce-La-O mixed oxide catalyst for methane combustion is related to superoxide ions and surface reducibility. (C) 2010 Published by Elsevier B.V.