Single-crystalline cx-MnO2 nanowires with diameters of 10-30 nm and lengths ranging from 6 to 10 mu m have been successfully synthesized by hydrothermal treating a mixed solution of KMnO4 and NH4Cl at 140 degrees C for 24 h. The final products were characterized by XRD, FESEM, TEM and HRTEM. The effect of anion Cl- in the possible rolling formation mechanism was also briefly discussed. (c) 2005 Elsevier B.V. All rights reserved.