Cyanobacteria, as a renewable source of carbon, was used to prepare activated carbon electrodes in supercapacitors. The activation includes a pre-carbonization at 400 °C followed by KOH heat treatment at 800 °C, leading to efficient and high degree of graphitization. The activated carbon electrode consisted primarily of carbon and oxygen, and possessed a large specific surface area of 2184 m2 g-1, with pore size centered at 27 nm. In 6 mol L-1 KOH electrolyte, the electrode exhibited superior specific capacitance of 271 F g-1 and 222 F g-1 at a charge/discharge current density of 0.1 A g-1 and 5.0 A g-1, respectively. The results demonstrated that the activated carbon derived from cyanobacteria can serve as promising electrode material for electrical double-layer capacitors.