In this study the influence of SnOx nanoparticles on the catalytic performance of alumina-supported gold catalysts was investigated in CO oxidation. The tin modified supports were prepared by grafting of tetraethyltin onto the surface of alumina via its hydroxyl groups. The decomposition of organometallic surface species in oxygen yielded highly dispersed tin oxide on the surface of alumina. Gold was introduced onto the tin modified alumina support by both deposition-precipitation with urea and direct anionic exchange techniques using HAuCl4 solution. Based on catalytic and different spectroscopic measurements it is suggested that the presence of "Snn+-Au ensemble sites" is responsible for the increased activity of these catalysts. (C) 2009 Elsevier B.V. All rights reserved.