A series of Se-modified Ru/C (Se-Ru/C) samples were prepared from a carbon-supported ruthenium precursor. Selenium was incorporated by two different methods; in the first case, Se was incorporated by treating the Ru/C precursor in a selenious acid solution followed by reduction in H-2 atmosphere. In the second case, Se was incorporated to Ru/C by means of thermal treatment in a selenium atmosphere. The samples thus obtained were characterized by different techniques: X-ray diffraction, energy dispersive X-ray spectroscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. A detailed study has been made of the structural properties and chemical composition of the different Se-Ru/C samples. Microscopy results reveal that Se is incorporated homogeneously, being preferentially located on the surface of the Ru atoms. These results agree well with XRD and XPS data. The incorporation of Se in the lattice results in the formation of RuSe2 only if RuO2 already exists. On the contrary, if Ru is in its metallic form, Se remains as an amorphous layer located on the surface of the Ru particles. The performance of the catalysts on the oxygen reduction reaction was evaluated either in the absence and presence of methanol. Se-containing samples develop more active and methanol tolerant catalysts, particularly when Se is located on the surface of the Ru particles. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.