The Ce(0.8)y(0.2)O(1.9) solid solution was prepared by nitrate sol-gel method, and a series of catalysts with different PdO loading were prepared using impregnation method. These catalysts were characterized by XRD, Raman, CO-TPR, CO2- and O-2-TPD techniques. The PdO is highly dispersed on the surface of the solid solution when the loading is lower than 0.5 wt.%. As PdO loading increases to 2 wt.%, it begins to form the crystalline structure. CO2-TPD profiles show that the CO adsorbed on highly dispersed PdO is more easily oxidized to CO2 than that adsorbed on crystalline structure and O-2-TPD results indicate that it is more difficult to decompose for highly dispersed PdO than that for crystalline structure. CO-TPR profiles show that the highly dispersed PdO is easily reduced. Catalytic activities of these catalysts for CO and CH4 oxidation indicate that both the highly dispersed and crystalline PdO are the active site for CO oxidation, while the crystalline structure is the active site for CH4 oxidation. (c) 2006 Elsevier B.V. All rights reserved.