In this paper, the support surface properties (surface oxygen-containing functional groups and structure defects) of porous carbon spheres (PCSs) were carefully designed by as UV assisted O₃ technology. CO catalytic oxidation reactions performed over the supported Pd-Ce catalysts on modified porous carbon spheres. Results illustrated that the Pd-Ce/PCSs catalysts exhibited high CO catalytic activity, which were increased at first, and then decreased with UV assistant-O₃ treatment time. The Pd-Ce/PCSs-30 catalyst exhibited superior activity and T₁₀₀ was only 15 °C. Moreover, the Pd-Ce/PCSs-30 catalyst obtained an excellent stability, and 100% CO conversion could be maintained as the time on stream evolutes up to 16h in the presence of H₂O in the feed. Based on characterization results, there were two main factors: (a) the surface area and pore volume were decreased with UV-O₃ treatment, leading to the enhancement of Pd-Ce particle size, and the decrease of Pd-Ce nanoparticle dispersion and mass transfer efficiency, as well as the decrease of catalytic activity of Pd-Ce/PCSs, (b) the surface oxygen content and defect sites of PCSs were raised by UV-O₃ treatment, which could improve surface loading of Pd, Ce and enhance PdOCe bonding interactions, thereby increasing the activity of Pd-Ce/PCSs.