The novel and efficient bismuth modified supported Co-Mn catalysts were prepared and employed to catalyze the preferential oxidation of CO (CO PROX) in simulated syngas. The effects of introducing-methods and loadings of bismuth on both catalytic performance and catalyst nature were investigated. The N-2 adsorption/desorption measurement, X-ray diffraction (XRD) and H-2-temperature programmed reduction (H-2-TPR), and O-2-TPD (O-2-temperature programmed desorption) characterization techniques were performed to reveal the relationship between the catalytic properties and the nature of the catalysts. Results demonstrate that the as-prepared Bi modified supported Co-Mn catalyst exhibits excellent catalytic performance, depending on the introducing method and loadings of Bi. The enhancement of Bi addition into supported Co-Mn catalyst in the catalytic performance for CO PROX reaction is mainly ascribed to the dramatically improved reducibility of the Bi modified sample. Moreover, the decrease in hydrogen transformation over the Bi modified samples can be observed, suggesting the introduction of Bi can compress the catalytic activity for hydrogen oxidation. This study definitely demonstrates the existence of synergistic effect between the added bismuth and Co-Mn/Ce0.85Zr0.15O2 in the Bi modified supported Co-Mn catalyst for CO PROX reaction. The developed Co3O4-MnOx/Ce0.85Zr0.15O2-Bi2O3 catalyst with bismuth content of 4.2 wt.% presents the outstanding catalytic activity, selectivity, and durability for CO PROX reaction in the simulated syngas, and it can be considered as a promising candidate for highly efficient CO elimination from H-2-rich stream. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.