Activated carbons (ACs) from petroleum coke by microwave heating KOH activation are treated by microwave to investigate the effect of microwave−treatment power on AC properties. The electrochemical properties of AC electrodes for supercapacitors were investigated by cyclic voltammetry, constant current charge−discharge and electrochemical impedance spectroscopy. The results showed that specific surface area (SBET) and total pore volume of microwave−treated ACs, specific capacitance and energy density of microwave−treated AC electrodes decreased. The electrical conductivity and stability of AC electrodes for supercapacitors were improved. Fast microwave−treatment is an efficient method to obtain suitable ACs for supercapacitors.