The oxidation of carbon monoxide adsorbed on Fe-n (n = 1-6) clusters is studied using density functional theory. Both neutral and anionic clusters are studied. The reactions of chemisorbed CO with O-2 are found to be highly exothermic for all of the iron clusters considered. Effects of higher coverages are estimated using the Fe-4 cluster with two adsorbates. namely Fe-4(CO)(2), Fe4C2, and Fe4O2 clusters. Our results suggest that the iron clusters sustain a full catalytic cycle of carbon monoxide oxidation. Published by Elsevier B.V.