The preferential oxidation of CO in H-2-rich gas was studied over gold catalysts supported on ceria modified by rare earths (RE = La, Sm, Gd and Y). The ceria supports were prepared by mechanochemical activation or co-precipitation. The amount Of RE2O3 was 10 wt%. Gold (2 wt%) was added by the deposition-precipitation method. The samples were characterized using XRD, HRTEM, HAADF, TPR, and Raman spectroscopy. It was established that catalysts prepared by co-precipitation were more active than samples made by mechanochemical activation. A gold catalyst on yttrium-modified ceria, prepared by co-precipitation, exhibited the highest catalytic activity and selectivity, and high stability. No substantial differences in the size distribution and average size of the nanogold particles in the studied catalysts were observed. The main reason for the differences in PROX activity of these gold catalysts was searched into the role of the ceria supports, depending on the preparation method, and the nature of the modifier. (C) 2009 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.