Mesoscopic WO3 microspheres composed of self-assembly nanofibers were prepared by hydrothermal reaction of tungsten acid potassium and H2O2. The mesoscopic WO3 microspheres offer desired porous properties and large effective active areas provided by intertwining nanofibers, thereby resulting in excellent supercapacitive properties due to facile electrolyte flow and fast reaction kinetics. In three electrode configuration, mesoscopic WO3 microspheres exhibit specific capacitance value of 797.05 Fg(-1) at the current density of 0.5 Ag-1 and excellent cycling stability without decay after 2000 cycles in 2 M H2SO4 aqueous solution. These values are superior to other reported WO3 composites. An asymmetric supercapacitor is constructed using the as-prepared WO3 mesoscopic microspheres as the positive electrode and the activated carbon as the negative electrode, which displays excellent electrochemical performance with a maximum energy density of 97.61 Wh kg(-1) and power density of 28.01 kW kg-1. These impressive performances suggest that the mesoscopic WO3 microspheres are promising electrode materials for supercapacitor. (C) 2015 Elsevier Ltd. All rights reserved.