A facile method was demonstrated for the preparation of Pt3Ni alloy nanoparticles supported on a sandwich-like graphene sheets/carbon nanospheres/graphene sheets substrate (Pt3Ni-C/rGO) through a one-pot solvothermal process in N,N-dimethylformide without the addition of reducing agents and surfactants. Transmission electron microscopic measurements showed that carbon nanospheres were homogeneously dispersed in the matrix of exfoliated graphene sheets, and Pt3Ni nanoparticles were distributed on the graphene surfaces without apparent agglomeration, where the average core size was estimated to be 12.6 +/- 2.4 nm. X-ray photoelectron spectroscopic studies demonstrated that electron transfer likely occurred from the Pt3Ni alloy nanoparticles to the graphene sheets. Electrochemical measurements showed that the mass activity of the Pt3Ni C/rGO catalysts in methanol oxidation was 1.7-times higher than that of Pt3Ni nanoparticles supported on reduced graphene oxide alone (Pt3Ni/rGO), and 1.3-times higher than that of commercial Pt/C (20 wt%). Additionally, CO tolerance and durability were also remarkably enhanced. These superior electrocatalytic activities were attributed to the following major factors: (i) the insertion of carbon nanospheres into the graphene matrix prevented restacking/refolding of the graphene sheets, leading to an increasing number of accessible active sites as well as transport channels for mass and charges; and (ii) the synergetic effect between Pt3Ni nanoparticles and rGO weakened the bonding interactions with reactant species, as manifested by the enhanced kinetics of methanol oxidation and CO oxidative desorption. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.