The angular and velocity distributions of desorbing product CO 2 were studied in the CO oxidation on a stepped Pt(112) = (s)3(111) (001) surface by means of angle-resolved thermal desorption combined with a cross-correlation time-of-flight technique. The desorption occurs mainly along the terrace normal, indicating predominant CO 2 formation on the terrace. The translational temperature of this CO 2 is maximized to 1330 K around the terrace normal. On the other hand, the angular distribution becomes asymmetric at small CO coverages when the desorption angle is varied perpendicularly to the step edges. This indicates a new component collimated at the desorption angle of -25°. It is assigned to the desorption from step sites. The maximum translational temperature of this CO 2 is 1190 K. The desorption of CO and oxygen shows a simple cosine distribution, providing no structural information.