The reaction kinetics and dynamics of carbon monoxide oxidation on a stepped Pt(113) = (s)2(111) x (001) surface were studied by angle-resolved kinetic and velocity measurements at the steady state. CO2 desorption sharply collimated nearly along either the (111) site normal or the (001) site normal. Only two reaction sites, the (111) and (001) sites, were operative. The translational energy of CO2 was characteristic of each site throughout a site switching. At surface temperatures above 520 K in the active region, where the reaction was first order in CO, the preference of the (111) site was suppressed with increasing CO pressure. Below 520 K, on the other hand, site switching slowly took place under limited conditions, in which both sites considerably contributed to the reaction and a meta-stable adsorbed phase seemed to be formed. The preference for the (111) site over the (001) site was caused by the former＇s higher reactivity of oxygen.