The behaviours of irreversible adsorption (IRA) of Sn adatoms on Pt(100), Pt(111) and Pt(110) electrodes were characterized using cyclic voltammetry. It has revealed that Sir can adsorb irreversibly on Pt(100) and Pt(111), while not significantly on Pt(110) electrode. Quantitative analysis of the relationship between 1 - theta(H) and theta(Sn) suggests that Sn adatoms may adsorb preferably on hollow sites of Pt(111) (threefold) and Pt(100) (fourfold) planes, which is in accordance respectively with the values 0.31 and 0.21 of coverage of IRA Sn adatoms in saturation adsorption determined on these electrodes. The IRA Sn adatoms on different basal planes of Pt single crystal yield different impact on the electrocatalytic oxidation of ethanol. It has revealed that the IRA Sn adatoms on Pt(100) electrode have declined the activity for ethanol oxidation, while IRA Sn adatoms on Pt(111) have enhanced remarkably the electrocatalytic activity with Sn coverage theta(Sn) between 0.09 and 0.18. The oxidation peak potential E-p and the current density j(p) of ethanol oxidation on Pt(111)/Sn were varied with theta(Sn), and the highest j(p) (1258 mu A cm(-2)) as well as the lowest E-p (0.20 V) were measured simultaneously at theta(Sn) around 0.14. In comparison with the data obtained on a bare Pt(111), the E-p was shifted negatively by 65 mV and the j(p) has been enhanced to about 1.7 times on the Pt(111)/Sn (theta(Sn) = 0.14), which is ascribed to hydroxyl species adsorption at relatively low potentials on Pt(111)/Sn surfaces. The current study is of importance in revealing the fundamental aspects of modification of the basal planes of Pt single crystal using Sir adatoms, and the impact of this modification on electrocatalytic activity towards ethanol oxidation. (C) 2008 Elsevier Ltd. All rights reserved.