Three-dimensional (3-D) MnO-carbon nanotube (CNT) nanocomposites were prepared by a simple one-pot hydrothermal method. An electrode was then prepared with these nanocomposites. For comparative investigation, MnO microspheres were also hydrothermally prepared without adding CNTs. The as-synthesized MnO microspheres were then mechanically mixed with CNTs to prepare a subsequent electrode. The samples were characterized by electron microscopy, X-ray diffraction, and electrochemical methods. It has been revealed that a 3-D conductive network of CNTs was formed with microspheres of MnO nanorods interwoven with and connected by CNTs. As a result, the hydrothermally mixed MnO-CNT electrode showed a higher specific capacitance than the mechanically mixed electrode. It has therefore been concluded that the hydrothermal mixing method yields a more homogeneous product that is better suited to take full advantages of both the high capacitance of MnO and the high electrical conductivity of CNTs. The 3-D MnO-CNT nanocomposites reported herein have provided a promising electrode material for supercapacitors and other electrochemical energy storage/conversion devices. © 2010 Elsevier B.V. All rights reserved.