Pt catalysts supported on Al2O3, CeO2/Al2O3, Na2O/Al2O3, and K2O/Al2O3 were prepared and characterized with respect to surface area, CO chemisorption, temperature-programmed desorption (TPD) of CO2, and temperature-programmed reduction (TPR) of H2. The effects of basic additives on Pt/Al2O3 for carbon monoxide and propylene oxidation were investigated. The reactions were performed under the stoichiometric and oxygen-deficient conditions. The addition of basic additives slightly decreases the surface area of the catalyst and does not significantly change Pt dispersion. The addition of basic additives also influences the reducibility of Pt/ Al2O3. The basicity of the catalyst is in the order Pt-K2O/Al2O3 > Pt-Na2O/Al2O3 > Pt-CeO2/ Al2O3 > Pt/Al2O3. The promoted Pt/Al2O3 catalysts are much more active than the unpromoted one for CO and C3H6 oxidation under the stoichiometric point. Under oxygen-deficient conditions and in the absence of water, C3H6 conversions on all catalysts studied herein increase with increasing reaction temperature. Nevertheless, this phenomenon contrasts with CO conversion once oxygen is completely reacted. Pt/Al2O3 exhibits the highest C3H6 conversion and the lowest CO conversion among these catalysts, and the addition of CeO2, Na2O, and K2O on Pt/Al2O3 can promote the CO conversion. Under oxygen-deficient conditions and in the presence of water, the water-gas shift and steam re-forming reactions can take place and result in increases of CO and C3H6 conversions. Pt/Al2O3 is the most active catalyst for the steam re-forming reaction and the lowest active catalyst for the water-gas shift reaction among these catalysts. Nevertheless, the addition of basic additives on Pt/Al2O3 catalyst can significantly enhance the water-gas shift reaction that can reduce CO emission. The promotional effect is in the order K2O > Na2O > CeO2, that is the same order as the basicity of the promoted catalysts. Additionally, K2O could be a promising additive to a catalytic converter of a two-stroke motorcycle since it can significantly enhance CO conversion.