The oxygen reduction reaction (ORR) was studied on carbon-supported cubic palladium nanoparticles of different sizes (similar to 30 nm, similar to 10 nm and similar to 7 nm). Cetyltrimethylammonium bromide (CTAB) and polyvinylpyrrolidone (PVP) were used as capping agents to prepare the nanocubes and Pd content in the catalyst samples was 20 and 50 wt%. The surface morphology of the prepared materials was studied by transmission electron microscopy (TEM). The catalyst materials were electrochemically characterised by cyclic voltammetry and CO stripping experiments. The rotating disk electrode (RDE) method was employed for ORR studies in 0.5 M H2SO4 and 0.1 M HClO4 solutions. The ORR results revealed that the specific activity of cubic Pd nanoparticles is higher than that of spherical Pd particles and does not depend on the Pd content in the catalyst, but decreases with decreasing the size of Pd nanocubes. Mass activity of Pd nanocubes increased with decreasing the particle size. The ORR proceeds mainly via 4-electron pathway and the reaction mechanism is similar to that on bulk Pd. (C) 2015 Elsevier Ltd. All rights reserved.