In this research, a rapid and controllable synthesis of octahedral Mn(OH)(2) nanoparticles with a size range from 140 to 200 nm has been done by a sonochemial irradiation method for the energy storage applications. Transmission electron microscopic images, energy disperse X-ray spectroscopy (EDX), X-ray photo electron spectroscopy (XPS), X-ray diffraction (XRD), and Fourier transform infrared (FUR) analyses clearly indicate the formation of octahedral Mn(OH)(2) nanoparticles. Octahedral Mn(OH)(2) nanoparticles were evaluated as a supercapacitor material that exhibits specific capacitance 127 F g(-1) at a current density of 0.5 mA cm(-2) in the potential range from -0.1 to 0.8 V in 1 M Na2SO4 solution. (c) 2013 Elsevier Ltd. All rights reserved.