We have synthesized 1D nanowires of lithium nickel manganese oxides with two different crystal structures through the chemical oxidation reaction of solid-state precursor LiMn0.5Ni0.5O2 under hydrothermal condition. According to X-ray diffraction and elemental analyses, the nanowires obtained by persulfate treatments at 65 and 120°C crystallize with a hexagonal layered and an α-MnO2-type structure, respectively, in which nickel and manganese ions exist in octahedral sites. Electron microscopic analyses reveal that the platelike crystallites of the precursor are changed into nanowires with the diameter of ∼20nm after the persulfate treatment. Thermal and infrared spectroscopic analyses clearly demonstrate that, in comparison with α-MnO2-structured nanowires, the hexagonal layered nanowires contain less water molecules in the lattice, which makes them suitable for the application as electrode materials for lithium secondary batteries. According to electrochemical measurements, the hexagonal layered nanowires show a larger discharge capacity and an excellent cyclability with respect to repeated Li intercalation–disintercalation process. X-ray diffraction and electron microscopic analyses on the samples subjected to electrochemical analysis reveal that the layered structure and 1D morphology of the nanowires are still maintained after the electrochemical cyclings, which is responsible for their excellent electrochemical performances.