In this study, a novel electrode material, modified activated carbon aerogel, has been developed for electric double-layer capacitors (EDLCs). This novel material was produced by the activation of carbon aerogel under CO2 flow, followed by surface modification with a surfactant, sodium oleate. It has been characterized by BET measurement and BJH method for its surface area and pore-size distribution, and by constant-current charge–discharge technique, cyclic voltammetry and electrochemical impedance spectrum (EIS) for its specific capacitance, equivalent series resistance and power capability. It was found that, after the surface modification, the wettability of the organic electrolyte based on non-polar organic solvent (i.e., propylene carbonate) to the activated carbon aerogel was improved greatly, which resulted in a lower internal resistance and a higher usable surface area. As results, a higher specific capacitance, energy density and power capability were achieved for the capacitor using the modified activated carbon aerogel electrodes than those without the surface modification. The effects from the surface modification became more significant at higher charge–discharge rates, at which the wettability of the electrolyte to the electrode material usually becomes more important and critical.