Developing means of controlling the composition of bimetallic Pt-Sn catalysts by appropriate preparation is important for their electrocatalytic activity. In this study, a polyalcohol method has been applied to synthesize graphene-supported Pt-Sn catalysts in different ethylene glycol/water mixtures, and the effect of water content on the composition of the catalysts has been investigated. Microstructural analysis has revealed the onset of aggregation of catalyst particles and increasing Sn content with the increase of water content. In terms of the electrocatalytic properties, the electrochemical activity of Pt-Sn/graphene for the ethanol oxidation reaction was improved with increasing Sn content due to the bifunctional mechanism and ligand effects. The activity of the catalyst was maximized at a water content of 5 vol.%. On further increasing the water content, a substantial decrease in the electrochemically active surface area (ECSA) was incurred due to blocking by tin oxide and the aggregation of catalyst particles, and the activity of the catalysts decreased. (C) 2014 Elsevier Ltd. All rights reserved.