A comparative study of catalytic CO oxidation and selective CO oxidation over Pt/Al₂O₃ and CeO₂-promoted Pt/Al₂O₃ catalysts has been investigated for the removal of a trace amount of CO from the reformed gas. The catalysts were prepared by sol gel and incipient wetness impregnation. CO oxidation and selective CO oxidation were carried out with a 5%Pt/Al₂O₃ and a 5%Pt/15%CeO₂/Al₂O₃. The presence of 15%CeO₂ inthe 5%Pt/Al₂O₃ dramatically improves the activities to CO oxidation and selective CO oxidation at low temperature (<180℃). FTIR results indicate that CO could react with lattice oxygen from ceria and release CO₂ as a product. Low space velocity would obtain high CO conversion at low temperatures while high space velocity would obtain high CO conversion at high temperatures. The results also show that a 5%Pt/15%CeO₂/Al₂O₃ can completely oxidize 1% CO at180℃with selectivity of 52% and space velocity of70,000 cm³·g^-1·h^-1. Under the realistic gas feed with 1%O₂, this catalyst is very stable and retains its activity and selectivity at180℃during 72 h.