The roles of Ru and Sn in mesoporous PtRu and PtRuSn alloys for ethanol electrooxidation reaction were investigated. The catalyst samples were prepared via co-reduction of metal precursors in an aqueous domain of lyotropic liquid crystalline phase of a nonionic surfactant. The crystallite sizes, obtained from x-ray diffractograms of mesoporous PtRu and PtRuSn catalysts, were approximately the same at 3.6 nm. There was a good agreement between the measured lattice parameter and the one calculated from a modification of Vegard's Law suggesting that the ternary PtRuSn alloy had formed. From XPS analysis, the surface species of Ru in both catalysts is in metallic form while Sn in PtRuSn is in SnO phase. The electrochemical measurements in ethanol solution revealed that PtRuSn had exhibited a lower onset potential by about 0.1 V, and also produced a significantly higher oxidation current density than had PtRu. In addition, the chronoamperometry tests demonstrated a lower poisoning rate for ethanol oxidation on the PtRuSn surface at the low potential of 0.3 V vs RHE. However, the adsorbed poisoning species had been effectively oxidized from the surface of PtRu, and consequently shown to be the most poison-tolerant catalyst at a high potential of 0.6 V and a high temperature (60 degrees C). As a result, Ru and Sn addition exhibited different promotional effects for ethanol oxidation. The addition of Sn promoted dissociative adsorption of ethanol molecules, while the addition of Ru activated the water molecules, which was followed by the oxidation of the strongly adsorbed CO. The added Ru and Sn had enhanced the overall ethanol oxidation on the PtRuSn catalyst. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.