Polydivinylbenzene (PDVB) is hybridized inside nanosized pores of activated carbon (AC) via radical polymerization. The amount of PDVB is varied by changing the adsorbed amount of divinylbenzene (DVB). The pore size of AC is less than 4 nm and DVB is adsorbed inside the AC pores without any organic solvents. The DVB-adsorbed AC is mixed with a radical initiator, 2,2'-azobisisobutyronitrile (AIBN), and the mixture is heated for polymerization. Unpolymerized DVB and AIBN-derived impurities are removed from the resulting AC/PDVB hybrids by vacuum heating. Absence of PDVB on the outer surface of AC particles is confirmed by scanning and transmission electron microscopies. A nitrogen adsorption/desorption measurement of the hybrids show that their specific surface areas as well as micro-and mesopore volumes linearly decrease with increasing the amount of the hybridized PDVB. Their electric double-layer capacitor (EDLC) performance is evaluated by electrochemical measurements using aqueous H2SO4 electrolyte. The results reveal that their capacitances and rate capabilities decrease with increasing the amount of the hybridized PDVB. These results suggest that the hybridized PDVB exist as agglomerates uniformly inside micropores and mesopores despite the amount of PDVB.