Pt-SnOx/C catalysts were prepared in a polyol process under Ar, sequential Ar and air, and air atmospheres in combination with a high temperature reduction treatment. The composition, structure, morphology and oxidation state of the prepared catalysts were characterized by Inductively Coupled Plasma-Atom Emission Spectroscopy, X-ray diffraction, scanning transmission electron microscopy and X-ray photoelectron spectroscopy. The electrochemical activities were evaluated by CO stripping voltammetry and single cell test in combination with in situ IR reflection absorption spectroscopy (IRRAS). The polyol-synthesized Pt-SnOx/C catalysts prepared under different atmospheres had a similar bulk composition, particle size and lattice parameter, however, the Pt-SnOx/C catalyst prepared under Ar atmosphere possessed a greater proportion of Sn(II) species than the other Pt-SnOx/C catalysts. Electrochemical and in situ IRRAS measurements indicated that the Pt-SnOx/C catalyst under Ar atmosphere had the greatest CO tolerance in proton electrolyte fuel cell among the Pt-SnOx/C catalysts. (C) 2010 Elsevier B.V. All rights reserved.