Carbon black (CB)/manganese dioxide (MnO2) composites are prepared by a sonochemical method from an aqueous solution of potassium bromate and manganese sulfate. The morphology, structure, physical properties and specific surface area of samples are examined by scanning electron microscopy (SEM), transition electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and Brunauer-Emmett-Teller (BET) method. Electrochemical properties of the synthesized composites with different carbon to manganese dioxide ratios are studied by cyclic voltammetry (CV), galvanostatic charge-discharge, and electrochemical impedance spectroscopy (EIS). Electrochemical data for the composites obtained in the 0.5 M Na2SO4 solutions show the capacitive behavior in the voltage window of 0-1.0 V versus Ag/AgCl. When the mass ratio of MnO2 composite material is 65 wt% the specific capacitance of CB-MnO2 composite calculated from the CV curves is 313 F g(-1) at the scan rate of 5 mV s(-1) whereas specific capacitance for pure gamma-MnO2 prepared in the same conditions is 257 F g(-1) at the scan rate of 5 mV s(-1). The CB-MnO2. composites show higher energy density than pure gamma-MnO2. Also, they show a long cycle life in the potential range of 0-1.0 V and retain 78.3% of initial capacitance over 1000 cycles. (C) 2013 Elsevier B.V. All rights reserved.