SnO2-modified PtRu/C catalysts were prepared in a polyol process to investigate the effect of a SnO2 deposition sequence on the catalytic activity for methanol electro-oxidation. The structure, morphology, and chemical state of the prepared catalysts were characterized by X-ray diffraction, scanning transmission electron microscopy, and X-ray photoelectron spectroscopy. The electrochemical activities were evaluated by cyclic voltammetry, linear sweep voltammetry, and chronoamperometry measurements in combination with in situ IR reflection-absorption spectroscopy (IRRAS). Compared with those in the PtRu/C catalyst, a simultaneous deposition of PtRu and SnO2 particles or a deposition of SnO2 prior to PtRu improved the metal dispersion and decreased the alloyed Ru fraction. The deposition sequence of SnO2 did not alter the chemical-state distribution of Pt and Ru but resulted in a different surface atomic ratio of Pt, Ru, and SnO2. Electrochemical and in situ IRRAS measurements indicated that the SnO2-modified PtRu/C catalyst prepared by the deposition of PtRu prior to SnO2 gave the best catalytic activity for COads and methanol electro-oxidation among the PtRu/C and SnO2-modified PtRu/C catalysts. The roles of SnO2 deposited with different sequences in the SnO2-modified PtRu/C catalysts were proposed. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3133249] All rights reserved.