Downsizing the Pt particle to the atomic level in the electro-catalysts is highly desirable to enhance its utilization efficiency in fuel cells. In this study, Pt subnano/nanoclusters were stabilized by the pristine graphene nanosheets (GNSs) derived from chemical vapor deposition and the resulting Pt/GNS hybrids were examined as catalysts for electro-oxidation of alcohols (methanol, ethanol, ethylene glycol and glycerol). In spite of the strong hydrophobic surface, the GNS was proved to be a promising catalyst support because the edges and defects in the GNS could effectively anchor and stabilize the Pt subnano/nanoclusters. The Pt/GNS catalyst showed an extremely high electrochemical active surface area and superior catalytic activity for alcohol oxidation compared with the commercial Pt/carbon black catalyst. The enhanced catalytic performance was attributed to the presence of the discrete Pt subnano/nanoclusters as well as the modulation of the electronic properties of Pt nanoparticles through the chemical interaction of Pt atoms with the edges and defects of the GNS support.