The performance and stability in long-term charge/discharge of a mesoporous resorcinol-acetaldehyde carbon cryogel as an electrode in an electric double-layer capacitor were evaluated with an organic electrolyte of 0.5 M LiClO4/PC (C4H6O3). Capacitance was found to increase as mesopore volume increased, and at all scan rates, the capacitance of mesoporous carbon CG-74 (74 indicates the concentration of catalyst at pH 7.4) was higher than that of commercial microporous activated carbon. CG-74 showed higher stability than microporous activated carbon, although performance decreased over the course of long-term charge/discharge measurement. The cause of this decline was examined by evaluating surface characteristics and pore structure. Deposition of lithium was seen at the cathode of microporous activated carbon, though no functional group was generated. Pore structure showed no decrease in pore volume due to deposition of lithium, and micropore volume was remarkably decreased in all samples. However, mesopore volume was not decreased, indicating that mesoporous carbon material CG-74 has better long-term stability. In terms of ionic diffusion and long-term stability, mesoporous carbon material CG-74 is superior to microporous activated carbon as an electrode material for use in an organic electrolyte.