Nanostructured manganese dioxide, MnO2, was synthesized by a sonochemical method. Nanostructured MnO2 had the shapes of flower-like and nanowires by changing the pH in the aqueous solution, as observed via scanning electron microscopy and transmission electron microscopy. The electrochemical capacitance was studied by cyclic voltammetry. A maximum specific capacitance of 300 Fg(-1) was obtained for the nanowires in a potential range from 0.1 to 0.9 V vs. SCE in 1 M sodium sulfate solution at a scan rate of 5 mV s(-1). These materials can be useful to increase the specific capacitance by wetting behavior of electrolytes from their structural properties. (C) 2010 Elsevier B.V. All rights reserved.