Polybenzimidazol (PBI) solutions of dimethyl acetamide (DMAc) were electrospun to be webs consisting of 250-nm ultra-fine fibers. The webs were carbonized, activated by steam, and resulted in activated carbon nanofibers (ACNFs). The average pore diameter and specific surface areas were 0.64-0.66 nm and 500-1220 m(2)/g, respectively. The specific capacitance from 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, micro pore volume, and resistivity of the samples. (C) 2004 Elsevier Ltd. All rights reserved.