The oxidation of carbon monoxide (CO) over PdRu solid solution nanoparticles was studied by the combined theoretical and experimental approaches. In this work, CO and O adsorptions on PdRu alloy surface models were theoretically investigated to understand the kinetics of CO oxidation reaction. It was found that CO adsorption on Pd atom in the PdRu alloy surfaces is weaker than on monometallic surfaces. From the experiment, reaction order of CO on the PdRu surface was observed to be smaller than that on Pd surface. While, the positive first order with respect to O-2 obtained for both Pd and PdRu alloy surfaces. Catalytic reaction mechanism is discussed on the basis of both theoretical and experimental observations.