By both density functional theory calculations (DFT) and voltammetry on rotating polycrystalline platinum disc, dimethylsulfoxide (DMSO) was investigated as a modifier of platinum electrocatalytic activity toward oxygen reduction reaction in aqueous solutions. The DFT calculations evidenced that DMSO molecule interacts with Pt surface most strongly by the mediation of S atom in SO group, and the modification of the surface electronic structure of Pt is restricted to the Pt atom contacting directly with the S atom. The calculated adsorption energy on Pt surface (Pt(100)) amounted to -108 kJ mol(-1). The voltammetry with polycrystalline Pt disk electrode in mixed H2O-DMSO solutions supported by 0.1 mol dm(-3) H2SO4 pointed out that DMSO adsorption suppressed oxide formation on Pt surface. In O-2-saturated solutions, in presence of 1 vol.% of DMSO, it was found that the rate of oxygen reduction reaction (ORR) was higher in comparison to the one measured in DMSO-free solution. It was also confirmed that adsorption of DMSO suppressed ethanol oxidation reaction in the entire potential window where ORR takes place. (C) 2013 Elsevier B.V. All rights reserved.