CO electrooxidation on a Pt-Ru/C catalyst was investigated in sulphuric acid electrolyte. The physico-chemical properties of the Pt-Ru/C catalyst were studied by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The influence of temperature, CO partial pressure and proton concentration on the electrochemical oxidation rate was investigated by steady-state galvanostatic polarization measurements. The apparent activation energy decreased from 70 to 30 kJ mol(-1) as the overpotential increased from 0.5 to 0.9 V vs NHE. The reaction order with respect to carbon monoxide increased, passing from 0.4 to 1, with the increase of the overpotential from 0.5 to 0.7 V vs NHE; a reaction order close to -1 with respect to the protonic concentration was observed, irrespective of the potential. Tafel slopes of about 136 mV dec(-1) were determined for oxidation of CO and CO/N-2 mixtures.