Poly(vinylidene fluoride)-derived ultramicroporous carbon with a specific surface area of 1012 m2 g−1 and a very narrow pore-size distribution peaked at 0.55 nm is investigated as electrode material for supercapacitors. The unique microstructure features enable the carbon to present not only a high gravimetric capacitance (264 F g−1) but also a high electrode density (0.826 g cm−3), resulting in an outstanding high volumetric capacitance of 218 F cm−3 in 6 mol L−1 KOH aqueous electrolytes. However, the carbon shows a very small capacitance of less than 7 F g−1 in 1 mol L−1 Et4NBF4/PC, which implies the pores are too small to be accessible even for the desolvated ions in the non-aqueous electrolyte.