The catalytic activity of Pt on alumina catalysts, with and without MnO x incorporated to the catalyst formulation, for CO oxidation in H 2 -free as well as in H 2 -rich stream (PROX) has been studied in the temperature range of 25–250°C. The effect of catalyst preparation (by successive impregnation or by co-impregnation of Mn and Pt) and Mn content in the catalyst performance has been studied. A low Mn content (2wt.%) has been found not to improve the catalyst activity compared to the base catalyst. However, catalysts prepared by successive impregnation with 8 and 15wt.% Mn have shown a lower operation temperature for maximum CO conversion than the base catalyst with an enhanced catalyst activity at low temperatures with respect to Pt/Al 2 O 3 . A maximum CO conversion of 89.8%, with selectivity of 44.9% and CO yield of 40.3% could be reached over a catalyst with 15wt.% Mn operating at 139°C and λ=2. The effect of the presence of 5vol.% CO 2 and 5vol.% H 2 O in the feedstream on catalysts performance has also been studied and discussed. The presence of CO 2 in the feedstream enhances the catalytic performance of all the studied catalysts at high temperature, whereas the presence of steam inhibits catalysts with higher MnO x content.