Low temperature CO oxidation was carried out over CeO2-TiO2 composite oxide and thereon supported Pd catalysts. The effects of Ce/Ti ratio and pre-treatments of calcination and reduction on the catalytic behaviour were investigated. The CO oxidation starts at about 220 degrees C over CeO2-TiO2 and the pre-reduction treatment has little influence on the catalytic activity. Pd supported on CeO2-TiO2 (Pd/CeO2-TiO2) exhibits high activity for CO oxidation and a complete conversion of CO to CO2 can be achieved even at ambient temperature, which suggests a synergistic effect between Pd and CeO2-TiO2. The activity and stability of Pd/CeO2-TiO2 can be further improved by the pre-reduction treatment. Ce/Ti ratio influences the catalytic behaviour significantly; the catalyst Pd/CeO2-TiO2 with a Ce/Ti mole ratio of 0.20 (Pd/Ce20Ti) owns the highest activity and stability, which suggests an optimization of the Pd-Ce-Ti interaction in Pd/Ce20Ti. The calcined Pd/Ce02-CeO2-TiO2 with a Ce/Ti mole ratio higher than 0.10 shows a distorted light-off profile with the temperature, which implies an alternation of the reaction mechanism with increasing temperature. (C) 2007 Elsevier B.V. All rights reserved.