Sn-modified platinum catalysts are presently one of the most active catalysts for the room temperature electrooxidation of ethanol at low potentials. In this study, Pt-Sn/graphene catalysts containing different ratios of Pt and Sn were prepared by the solution-phase reduction. Microstructural characterization shows that metallic Pt, Pt-Sn alloy and tin dioxide (SnO2) nanoparticles are distributed on the graphene sheets in the synthetic process. In terms of the electrocatalytic properties, graphene-supported Pt-Sn catalysts exhibit much higher current densities with increasing Sn proportions. Its proved that the addition of Sn not only decreases catalyst particles growth and agglomeration, but also promotes methanol electrooxidation by geometric effects on expanding Pt's lattice spacing, causing a synergistic effect between Pt and Sn nanoparticles. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.