Double-walled carbon nanotubes (DWCNTs)/delta-MnO2 composites were synthesized by a microwave irradiation method. The morphologies and microstructures of the samples were examined by scanning electron microscopy, transition electron microscopy and X-ray diffraction. Electrochemical properties were characterized by cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy. The microstructure observations indicate that the birnessite-type MnO2 mainly deposits inside the tubes at low MnO4- content, while on the surfaces of the tubes at high MnO4- content. As a result, DWCNTs-85%MnO2 composite exhibits high specific capacitance (240.2 F g(-1)) and good cycling stability (6.8% capacity loss after 2000 cycles). These results demonstrate that DWCNTs-MnO2 composites as electrode materials have potential application for high-performance supercapacitors. (C) 2011 Elsevier B.V. All rights reserved.