Pt10-xRux/C materials are synthesised using a classical polyol method and comprehensively characterised by thermogravimetric analysis, inductively coupled plasma – optical emission spectroscopy, electron transmission microscopy and x-ray diffraction. In N2-saturated electrolyte, the PtRu/C catalysts display lower onset potentials for adsorbed CO (COads) removal than the pure Pt/C one. Although the surface coverages of Pt by Ru are high, the PtRu/C catalysts display higher activity than the Pt/C one towards the hydrogen oxidation reaction (HOR), but the same mechanism occurs on all the catalysts. However, when the surface of the catalysts is saturated by COads, the HOR starts at a lower potential on Pt/C than on PtRu/C; Pt/C displays higher activity toward the HOR in the presence of COads between 0.40 and 0.55 V vs RHE. On Pt/C, a small part of COads desorbs into CO2 from 0.40 V through an Eley-Rideal mechanism, freeing very active Pt sites for the HOR. For potentials higher than 0.55 V vs RHE, the PtRu/C catalysts display higher activity for COads removal through the bifunctional mechanism. Ru atoms also block the most active Pt sites for the COads removal and the HOR.