Abstract: Due to coexisting of H2, CO2 and H2O with CO in hydrogen-rich gas produced from methanol reforming, the selective CO oxidation is companied with the side reactions of H2 oxidation, as well as CO or CO2 methanation and reverse water-gas shift reaction（RWGS）. This paper investigated the effects of the above side reactions on the selective CO oxidation over a 0.5% Pt/Al2O3 monolithic catalyst. The results showed that after 50% H2 is added into the reactants, the highest CO conversion is only 98.3% at 180℃ when the feed molar ratio of O2 to CO is 1, and the corresponding outlet CO concentration is 180×10－6. Adding 50% H2 into the reactants accelerate CO oxidation at low temperatures; the catalyst active reaction temperature window shifts down about 40℃. CO produced from RWGS is 80×10－6 at 200℃ indicating that the effect of RWGS on selective CO oxidation becomes obvious at temperatures higher than 200℃. On the other side, CO or CO2 methanation does not take place even at 300℃ under current conditions and has little effects on the selective CO oxidation.