Size controllable alpha-MnO2 nanowires were synthesized from KMnO4 and ethanol via a low-temperature hydrothermal route assisted with subsequently heat treatment. No acid or alkali was added. XRD and SEM results clarified alpha-MnO2 nanoparticles (5-30 nm) began to form at room temperature, and then grew up to nanowires (similar to 12 nm in diameter) when temperature increasing up to 120-160 degrees C for an appropriate reaction time. Otherwise, octahedron-like Mn3O4 began to form at 120 degrees C more than 4 h or at 160 degrees C more than 2 h. Hydrothermal-synthesized alpha-MnO2 show well thermal-stability even it was heated at 900 degrees C. And various size alpha-MnO2 nanowires were controllable prepared by adjusting heat treatment temperature of hydrothermal-synthesized alpha-MnO2 at range from 150 degrees C to 750 degrees C for 3 h, which show the strongest diffraction peak (211) plane. The capacity of hydrothermal-synthesized alpha-MnO2 at 120 degrees C for 2 h was about 125 F/g, which exhibited a promising electrochemical property. (C) 2015 Elsevier B.V. All rights reserved.