The selective oxidation of CO in hydrogen mixture was studied over Pt, Ru, and Pt-Ru bimetallic catalysts supported on alumina, ceria, or alumina impregnated with 10wt% ceria. The experiments were conducted at atmospheric pressure and in the temperature range of 50-400 ℃. Ceria was found to significantly promote the catalytic activity of the Pt catalysts by supplying oxygen to the metal interface, particulary at low temperatures where Pt alone was inactive. The Pt supported on pure ceria exhibited better low-temperature activity than the Pt supported on the alumina impregnated with ceria. When using chlorine compound as the metal precursor, the residual chlorine present on the catalyst was found to inhibit the oxygen mobility of the ceria to lower the catalytic activity. Ru also exhibited excellent low-temperature activities at temperatures lower than150 ℃. As to the preparation methods for the Pt-Ru bimetallic catalysts, the catalyst directly reduced under hydrogen at 300 ℃ without prior calcination exhibited better activity than the bimetallic catalysts prepared with a calcination step, indicating that the calcination step may hinder the formation of the alloy phase.