Electrically conducting carbon nanofiber (CNF) composite mats are prepared by electrospinning blended solutions of graphene oxide and polyacrylonitrile (PAN) in N,N-dimethylformamide (DMF), and their electrochemical properties are investigated as electrodes of supercapacitors. A graphene oxide concentration of 5 wt.% in a PAN polymer solution offers a large specific surface area and good conductivity after a carbonization process at 1000 degrees C. The supercapacitor electrode prepared with 5 wt.% graphene shows high specific capacitance, 146.62 F g(-1), and high energy density, 14.83-19.44 W h kg(-1), at power densities ranging from 400 to 20,000W kg(-1) in a 6 M KOH aqueous solution. (C) 2013 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.