A new MnOOH precursor route has been developed to synthesize single-crystalline nanorods of tetragonal beta-MnO2. Uniform gamma-MnOOH nanorods were first prepared by reducing KMnO4 with KI under hydrothermal conditions at 120 degreesC. After calcination of the gamma-MnOOH nanorods at 250 degreesC for 2 h in air, beta-MnO2 nanorods retaining the morphologies of gamma-MnOOH nanorods were obtained. The temperature, time and heating speed of calcination were found to be important for the morphologies of the beta-MnO2 nanorods. (C) 2004 Elsevier Ltd. All rights reserved.