Activated carbon fiber cloth (ACFC) electrodes with high double layer capacitance and good rate capability were prepared from polyacrylonitrile (PAN) fabrics by optimizing the carbonization temperature prior to CO2 activation. The carbonization temperature has a marked effect on both the pore structure and the electrochemical performances of the ACFCs. Moderate carbonization at 600°C results in higher specific surface area and larger pore size, and hence higher capacitance and better rate capability. The specific capacitance of the ACFCs in 6molL−1 KOH aqueous solution can be as high as 208Fg−1. It remains 129Fg−1 as the current density increases to 10000mAg−1.