beta-MnO2 single crystals with novel tetragonous morphology have been hydrothermally prepared in an HCl solution at 180 degrees C for 24 h without using templates, catalysts, and organic reagents. The structure of the obtained beta-MnO2 was systematically investigated by X-ray diffraction, SEM and TEM microscopy, FT-IR spectroscopy, DSC-TGA analyses, and chemical compositional analyses. The morphology of beta-MnO2 could be controlled by the hydrothermal treatment temperatures and the hydrothermal reaction times. beta-MnO2 single crystals with diameters 200-600 nm and lengths up to 1-5 mu m not only had novel tetragonous morphology, but also had high purity. (c) 2006 Elsevier Ltd. All rights reserved.