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 0.64–0.66nm and 500–1220m2/g, respectively. The specific capacitance from the activated carbon nanofiber ranged from 125 to 178F/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.