The activated carbon was prepared from polyaniline by using electrochemical synthesis, subsequent carbonization and activation under the condition of mixed oxygen and nitrogen. The electrochemical measurements result showed that the activation led to better capacitive performances. The carbon reached a high specific gravimetric capacitance of 285Fg−1, with rectangular cyclic voltammetry curves at a scan rate of 2mVs−1 in 6.0molL−1 KOH solution, and it remained 83.7% even at a high scan rate of 50mVs−1. Furthermore, the porous carbon electrodes exhibited durable operation. After 10,000 cycles, the specific capacitance is still about 98.6% of the initial specific capacitance. These demonstrated that the activated carbon would be a promising electrode material for supercapacitors.