Carbon supported Pt, Ru and bimetallic Pt-Ru nanoparticles (Pt/C, Ru/C and Pt.Ru/C) have been prepared by the chemical reduction method. Particle morphology, composition and structure of nanoparticles have been investigated by scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis. SEM results showed a uniform dispersion of nanoparticles with rough and porous structure into carbon supports with the average particle size of 30-64 nm. EDX analysis demonstrated the presence of both Pt and Ru nanoparticles in each gas diffusion electrode. The Pt/C, Ru/C and Pt.Ru/C composites were used as electrocatalyst for oxygen reduction reaction (ORR) in alkaline media. The ORR activities of cathodes were characterized using cyclic voltammetry (CV), polarization technique, AC impedance spectroscopy (EIS) and chronoamperometry. CV and polarization curves showed significantly higher activity on Pt.Ru/C electrocatalyst than observed on Pt/C and Ru/C catalysts, which can be related to synergistic effect, which is playing a critical role in ORR activity. The Tafel slope values of 120 mV/dec showed that the first electron transfer is the rate determining step. The EIS results of cathodes under different polarization potentials indicated two different behaviours which depend on the applied dc potentials and reveal different electrochemical processes occurring on the electrodes. (C) 2015 Elsevier B.V. All rights reserved.