The oxidation of CO to form CO2 reaction proceeds via the combination of a chemisorbed CO molecule with a chemisorbed oxygen atom, the latter produced through the dissociative adsorption of Oa on the Pt surface. Due to the poisoning effect of the CO adsorption on the Pt surface, amount of adsorbed oxygen on the surface gains more importance. The aim of the study is to investigate the adsorption characteristics and the structure sensitivity of oxygen, hydrogen and carbon monoxide adsorption on Pt/y-AbOs catalysts. The surface structure of the catalysts was manipulated by increasing the particle size of the metals by increasing the calcination duration and temperature. As a result catalysts with the same metal loading but different surface composition in terms of edge, comer and low index plane atoms could be prepared. The zero coverage differential heat of adsorptions measured for CO and 2 do not show any change with the changing particle size. On the other hand, Ha shows a sharp decrease of zero coverage heat values as the average particle diameter of Pt increases. This can be concluded as Hz adsorption is more structure sensitive than the CO and $O_2$ adsorptions. The structure sensitivity of the CO oxidation reaction was confirmed by reaction experiments. In addition, it was observed that the reaction apparent activation energy decreased sytematically with increasing particle size.