Ce-Mo-Sn systems were studied for the catalytic oxidation of ethanol. The catalysts were obtained from precipitation of SnO(2)(.)xH(2)O in the presence of (NH4)(2)Mo7O24, with and without control of pH. Ce(NO3)(3) and (NH4)(2)Ce(NO3)(6) were used as Ce precursors, which were added to the system either by Mo-Sn impregnation or during coprecipitation. Mo and Ce concentrations were fixed at 9.2 and I wt.%, respectively, for every preparation. The solids were characterized by TPR and CO2 adsorption. The results indicate that cerium in Mo-Sn systems may be a poison or a promoter for ethanol oxidation. depending on the preparation method. Also, the results suggest that the formation of Ce species that behavior as promoters needs OH groups on the Mo-Sn surface.