Nanocomposites of intertwined multi-walled carbon nanotubes (MWCNTs) and MoO3 nanowires were synthesized using a hydrothermal method. The intercalation of MWCNTs with MoO3 nanowires made them excellent materials for viable supercapacitors with high energy and power densities. The specific capacitance of the intertwined MoO3-MWCNTs nanocomposite reached 210 F g(-1), and the energy density was improved greatly to 71.6 Wh kg(-1) with a power density of 600 W kg(-1) compared to those of pristine MWCNTs and MoO3 nanowires. The composite electrodes exhibited an excellent charge/discharge rate and long-term cyclic stability in terms of capacitance with an efficiency of more than 95% after 2000 cycles. These findings open up the possibility of intertwined MoO3-MWCNT composites being utilized in safe aqueous electrolyte (Na2SO4)-based high-voltage supercapacitors with high energy and power densities. (C) 2011 Elsevier Ltd. All rights reserved.