Abstract: The dependence of electric double layer capacitance on the pore structure of commercially available activated carbons in both nonaqueous and aqueous electrolytes was studied. Capacitance in the nonaqueous electrolyte (propylene carbonate solution of 1mol/L triethylmethylammonium tetrafluoroborate) was linearly related to that in the aqueous electrolyte (1mol/L H2SO4 solution). The contributions of the microporous surface area, Cmicro., and the surface formed on account of other large pores, Cext., were separately evaluated, the former being small and depending strongly on current density and the latter being almost constant.