A sequence of thermal treatments in oxygen was undertaken to study the influences of oxygen adsorption on the catalytic activity of SnO2 in CO oxidation. Commercial SnO2 (Fluka) and tin dioxide obtained from SnCl4 were characterized using XTD, BET, SEM TPD, and TPR methods. Catalytic activity of SnO2 samples was carried out as a function of pre-treatment temperature in oxygen. Due to the presence of different reactive oxygen forms, CO oxidation shows the hysteretic course. The approach to the differentiated mechanism of CO oxidation over SnO2 has been presented. The results obtained should be useful in understanding how the oxygen adsorption affects the catalytic activity of tin dioxide towards CO oxidation. (C) 2010 Elsevier B. V. All rights reserved.