Urchin-like alpha-MnO2 nanostructures were successfully synthesized via a simple hydrothermal process at different synthesis temperatures without using any template or surfactant. The microstructure and morphology of as-synthesized products were systematically investigated by focused ion beam, transmission electron microscopy, and high-resolution transmission electron microscopy. The electrochemical test of the prepared MnO2 exhibits ideal cyclic voltammetry behavior, high specific capacitance (151.5 F g(-1) at a current density of 1 A g(-1)) and excellent cycling stability (93.4% capacitance retention after 1000 cycles) which suggests its promising application as supercapacitor. (C) 2015 Elsevier B.V. All rights reserved.