High-quality ultra-long alpha-MnO2 nanowires, with diameter of about 25 nm and length of several hundred micrometers or even up to several millimeters, have been prepared using a simple hydrothermal approach without surfactants. By simple vacuum filtration, the superior flexible alpha-MnO2 paper with adjustable thickness has been produced, and displays an average modulus of 225 MPa at the thickness of 30 mu m. The crystallographic structure, chemical component and morphology of the alpha-MnO2 nanowires are characterized by XRD, FTIR, XPS, FESEM and TEM, respectively. The influences of NH4+ ion concentration and temperature on the crystallographic forms, morphological changes and aspect ratios of the alpha-MnO2 nanowires are systematically investigated. The as-prepared flexible alpha-MnO2 paper electrode exhibits a high specific capacitance of 118 F g(-1) at 2 mV s(-1) with excellent rate capability (42.4% at 200 mV s(-1)), and a superior cycling stability with only 4.7% loss after 1000 cycles. (C) 2013 Elsevier B.V. All rights reserved.