Mixed platinum-manganese oxide catalysts were prepared by impregnation of supported manganese oxide catalysts with a chloroplatinic acid solution. Supported manganese oxide catalysts used as bare catalysts were prepared from different manganese precursors (nitrate and acetate) and with two manganese loadings. Supported pure platinum catalysts were also prepared as a reference. The catalytic activity was evaluated in ethanol and toluene combustion. Considering the catalysts from the different manganese precursors separately, the catalytic activity increased with increasing platinum dispersion. The platinum dispersion was affected by the presence of basic sites on the surface. Furthermore, at least two different platinum active sites were found to exist on the surface. The sites corresponding to a direct platinum-Al2O3 interaction were more active than those corresponding to a platinum-manganese oxide interaction. Finally, the catalytic tests in the combustion of an ethanol-toluene mixture demonstrated that manganese plays a beneficial role in avoiding the inhibition of toluene combustion that is observed on pure platinum catalysts.