Effects of several preparation parameters on the physical properties and low-temperature CO oxidation activity of gamma -Al2O3 supported Pt-SnO2 catalysts were examined. Results obtained with different Pt and SnO2 loadings and ratios are compared on the basis of 1 wt% Pt/6 wt% SnO2/gamma -Al-2 O-3 which corresponds to an optimum atomic Pt:Sn ratio of 1:8. A space time of 15 mg min/ml gives the highest activity with no catalyst deactivation. Catalytic activity is enhanced in reaction mixtures containing excess oxygen (CO/O-2 = 1/2 or 1), while the stoichiometric feed ratio of CO/O-2 = 2 leads to catalyst deactivation and lower activity. Kinetic data show that low-temperature CO oxidation over 1 wt% Pt/6 wt% SnO2/gamma -Al2O3 is best described by a model based on oxygen adsorption on SnO2 followed by reverse-spillover from the oxide onto Pt sites and surface reaction occurring on Pt sites between chemisorbed CO and oxygen, with dissociative adsorption of oxygen as the rate-determining step.