Single-crystalline nanowires of hexagonal gamma-MnO2 phase have been prepared by a simple method in which the commercial granular gamma-MnO2 powders were hydrothermally treated in water or ammonia solution at 120-160 degreesC. The diameters of the gamma-MnO2 nanowires are 5-50 nm and the lengths up to several tens of micrometers. Calcination of gamma-MnO2 nanowires at the temperature range of 400-500 degreesC and above 600 degreesC results in, respectively, the production of single phases of beta-MnO2 and alpha-Mn2O3 crystals, while the nanofibrous morphologies persist. These 1-D nanostructured manganese oxides are expected to have possible novel properties and wide applications. (C) 2003 Elsevier B.V. All rights reserved.