KOH activation of microwave exfoliated graphite oxide (MEGO) is investigated in detail at temperatures of 450-550 °C. Out of the activation temperature range conventionally used for the preparation of activated carbons (>600 °C), the reaction between KOH and MEGO platelets at relatively low temperatures allows one to trace the structural transition from quasi-two-dimensional graphene platelets to three-dimensional porous carbon. In addition, it is found that nanometer-sized pores are created in the graphene platelets at the activation temperature of around 450 °C, leading to a carbon that maintains the platelet-like morphology, yet with a specific surface area much higher than MEGO (e.g., increased from 156 to 937 m(2) g(-1) ). Such a porous yet highly conducting carbon shows a largely enhanced electrochemical activity and thus improved electrochemical performance when being used as electrodes in supercapacitors. A specific capacitance of 265 F g(-1) (185 F cm(-3) ) is obtained at a current density of 1 A g(-1) in 6 m KOH electrolyte, which remains 223 F g(-1) (156 F cm(-3) ) at the current density of 10 A g(-1) .