The vibrational spectrum of carbon monoxide at the Pt/acetonitrile interface as a function of applied potential has been investigated using the surface-enhanced Raman spectroscopy technique. The electrolyte is 0.1 M LiClO4. The bands observed at ca. 506 and 2055 cm(-1) are attributed to the platinum-CO (v(pt-c)) and intramolecular C-O (vc-o) stretching vibrations, respectively, suggesting linearly adsorbed CO on platinum. The vpt-c band has an experimental Stark tuning rate of -4 cm(-1)/V, while the slope of vc-o band frequency versus potential approaches zero before the onset of electro-oxidation of COads, possibly resulting from low surface coverage of CO on platinum. The roughened Pt electrode surface has a high electrocatalytic activity, on which CO electro-oxidation occurs at ca. -0.7 V (vs Ag/Ag+). The main product of COads oxidation is confirmed to be carbonate due to the existence of trace water in the double-layer region as a source of oxygen for the reaction. It has also been found that the solvent acetonitrile can exert a chemisorbed decomposition reaction on the roughened Pt surface, while the adsorption of CO can significantly inhibit this reaction.