Nanostructured flower-like ε-MnO 2 and α-MnO 2 nanowires were prepared by themicrowave-assisted hydrothermalmethod at 110 °C and 140 °C. The ε-nanoflowers are about 500 nm in size and are composed of petals about 100 nm in length, while the α-nanowires are 20-30 nm in diameter and about 1 μm in length. The ε-MnO 2 demonstrates higher initial discharge capacity, while the α-MnO 2 shows greater cycling stability in different voltage ranges. Both phases of MnO 2 show better cycling performance in ethylene carbonate (EC)/diethyl carbonate electrolyte (DEC) than in EC/dimethyl carbonate (DMC) electrolyte. The ε-MnO 2 sample delivered a discharge capacity of 116.2 mAh g -1 for up to 100 cycles, indicating that it is a promising cathode material for lithium ion batteries. © 2012 The Chemical Society Located in Taipei & Wiley-VCH Verlag GmbH & Co. KGaA,Weinheim.