Two carbide-derived carbons (CDCs) were synthesized by chlorination from TiC at 600 and 1000 °C. These CDCs were treated by HNO3 solution and evaluated as supercapacitor electrode materials in an alkaline electrolyte. It is found that the structure in CDC synthesized at 600 °C is disordered carbon with micropores, whereas for the CDC synthesized at 1000 °C, the structure in it is mainly well-ordered graphitic structure with micro- and meso-pores. Due to the big difference of these two CDCs, HNO3 activation plays the different effects in structure and consequently the specific capacitance. CDC synthesized at 600 °C is easier to be activated with the same HNO3 concentration and the increase of specific capacitance with HNO3 concentration mainly caused by pseudocapacitance. For CDC synthesized at 1000 °C, HNO3 activation improves the wettability of it and the increased accessible surface area causes considerable increase in specific capacitance.