A new form of carbon nanofiber web was prepared that is considered to be a suitable material for the electrode of a supercapacitor exhibiting high capacitance. A polybenzimidazol/dimethyl acetamide solution was electrospun, and subsequently the web was steam activated at 700-900degreesC. The specific capacitance of the activated carbon nanofiber ranged from 125 to 178 F/g, depending on the activation temperature. The capacitance of the electrical double-layer capacitor was strongly dependent on the specific surface area, micropore volume, and resistivity of the samples. The results provide a simple and economical means that could substantially enhance the capacitance of carbon materials. (C) 2004 The Electrochemical Society.