The specific capacitance (F/g) of a poly(vinylidene chloride) (PVDC)-based electric double-layer capacitor (EDLC) carbon electrode prepared by heat-treatment at only 700 degreesC shows a capacitance as high as 64 F/g at 1 mA Output cur-rent density, although it shows a specific surface area of only 700 m(2)/g, smaller than those of other conventional activated carbon fibers and activated carbons. To elucidate the relationship between the specific capacitance and the pore structure for PVDC-based carbons, from an EDLC practical applications viewpoint, structural characterization was performed using various techniques. PVDC-based carbon had sufficient porosity during the carbonization process without any additional activation process for use as an EDLC electrode. It has been shown that the strongest peak in the pore size distribution is at a diameter around 9 Angstrom. The most probable electrolyte ion sizes, solvated as the hydrated SO42-ions in aqueous solution, have been obtained by computer simulation as 9 Angstrom. This range of electrolyte ion sizes is highly convenient for entering the pores of the present PVDC-based carbons to estabUsh the electric double layer at the pore wall. Furthermore the evolution of Cl-2 and HCl during the carbonization of PVDC creates rich open pores with nanometer dimensions connecting to the free surface of the particles in the samples. It is concluded that the higher specific capacitance of PVDC-based carbons, compared to conventional activated carbons in aqueous electronic double-layer capacitors, is due to their optimal pore size distribution. The present precursor has been shown to be a promising material for high power EDLC applications.