CO electrooxidation studies can be done in relation to either the poisoning effect in methanol fuel cells or to be applied as basis for the development of electrochemical CO sensors. In the present work, Pt and PtRu catalysts supported on multiwalled carbon nanotubes, CNTs, are probed with regard to their ability to detect changes in the CO concentration in acidic solutions. Pt and PtRu particles were dispersed onto pretreated CNTs by a modified polyol process using RuCl3 and H2PtCl6 as their metallic precursors. The physical characterization and dispersion of the catalytic particles were obtained through SEM and TEM images, and EDX analysis provided the chemical composition. CO oxidation was studied applying electrochemical techniques. For both catalysts, linear relationships were obtained when relating chronoamperometric current densities to different CO concentrations, indicating their possible application as CO sensors'devices materials. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.