We have reported a fast and eco-friend method to synthesize the MnO2 on catalytically grown carbon nanofiber (CGCNF). The CGCNF was functionalized by acid treatment under various H2SO4/HNO3 ratios. A microwave-assisted hydrothermal method was then used to synthesize MnO2/CGCNF composites at a very short time of 5 min. We demonstrated that the surface modification has significant effect on the MnO2 deposition and the electrochemical performance of the resulting MnO2/CGCNF composites. Electrical impedance spectroscopy analysis and cyclic voltammetry showed that O-functional group controls the electrical conductivity and the electrochemical performance of both CGCNF and CGCNF/MnO2 composites, respectively. It was found that C = O bond assists the MnO2 deposition. CGCNF/MnO2 composite showing specific capacitance (Csp) of 257 F/g at a scan rate of 5 mV/s and electrical resistance of 19 Omega was demonstrated. (C) 2016 Elsevier B.V. All rights reserved.