A Prussian blue/graphene (PB/GE) nanocomposite is synthesized as a non-precious metal catalyst by a spontaneous redox reaction in acidic solution with Fe powder, K-3[Fe(CN)(6)], and graphene oxide as precursors. The resulting PB/GE nanocomposite is characterized by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. The PB/GE nanocomposite-modified glassy carbon electrode (PB/GE-GCE) exhibits good electrocatalytic activity and long-term stability toward the oxygen reduction reaction (ORR). The reduced form of PB, Prussian white, has favorable electrocatalytic activity for the reduction of O-2 and H2O2 in acidic solutions. Rotating ring-disk voltammetric measurements clearly show that the dominant product of ORR at the PB-GCE is water produced by the 4e(-) reduction of O-2 at all potentials. ORR at the PB/GE-GCE occurs mainly inside the PB lattice through the 4e(-) reduction pathway at E > -0.5 V and on GE nanosheets through the "2 + 2" mechanism involving H2O2 as the intermediate product at E < -0.5 V. The PB/GE nanocomposite is a potentially efficient and cost-effective catalyst for fuel cells. (C) 2013 Elsevier B.V. All rights reserved.