The contribution of (Ce1-X Zr (X) )O-2 additives to alumina supports prepared by sol-gel and the catalytic properties of PdO/Al2O3-(Ce1-X Zr (X) )O-2 catalysts (similar to 0.3 wt% Pd, similar to 5 wt% (Ce1-X Zr (X) )O-2) in CO oxidation was herein investigated. The addition of (Ce1-X Zr (X) )O-2 to the support enhanced the surface area and decreased the size of Al2O3 particles. The UV-Vis bands of PdO particles and Pd2+ ions indicate that zirconia in (Ce1-X Zr (X) )O-2 promotes palladium-support interactions by forming highly dispersed PdO particles. Temperature-programmed reduction (TPR) in hydrogen revealed that ceria enhanced the redox capacity of the supports while zirconia lowered the reduction temperature of palladium oxide species. The comprehensive study revealed that the Ce/Zr ratio was a key factor influencing the catalytic activity of samples in CO oxidation, because palladium oxide-support interactions had a significant effect in changing of the reducibility of samples. So, the PdO/Al2O3-(Ce0.5Zr0.5)O-2 exhibited the highest catalytic activity.