Electrochemical oxidation of carbon monoxide between 0.3 and 0.5 V vs. RHE (reversible hydrogen electrode) was investigated in hot 0.005 M H2SO4-0.2 M Na2SO4 solution at 423 and 473 K under CO pressures ranging from 0.08 to 1.25 MPa. The reaction could be well explained by both the Langmuir-Hinshelwood mechanism for the reaction between carbon monoxide and water and the Langmuir isotherm for adsorption of carbon monoxide on a Pt electrode. Activation energy around 60 kJ.mol(-1) was observed. This value almost agrees with the apparent activation energy for electrochemical oxidation of methanol on a Pt electrode obtained between 393 and 463 K by Watanabe et al. (1997). We confirmed that CO adsorption decreases with the increase of temperature.