Hierarchically nanostructured composite electrodes were prepared by the electrodeposition of manganese dioxide nanowires (MnO2 NWs) with 5-20 nm diameters on electrospun carbon nanofiber (CNF) webs with diameters of 250 and 650 nm. The effects of CNF diameters and mass loading of MnO2 NWs on the hierarchical nanostructure formation and the performance of the composite electrodes were investigated. The internal structure of the composite electrode depended on CNF diameter and mass loading of MnO2 NW. The electrodes based on thinner CNFs and higher mass loadings of MnO2 NWs showed higher values of gravimetric and volumetric capacitances. This would be due to MnO2 NWs forming a dense network in the thinner three-dimensional CNF framework. In addition, asymmetric supercapacitors with the MnO2 NW/CNF composite electrode as the positive electrode and activated carbon as the negative electrode showed high energy and power densities of 8.9 W h kg(-1) and 4.9 kW kg(-1), respectively. These results clearly indicate that the hierarchical network nanostructure composed of an active material and a charge collector can be considered a promising electrode for various electrochemical devices.