Nitrogen-doped graphene is prepared by a solid microwave method with EDA (ethylenediamine) as the nitrogen source. The experimental results reveal that nitrogen atoms from the grafted EDA molecules on the surface of graphene are successfully doped into the lattices. The NGS (nitrogen-doped graphene nanosheets) sample exhibits outstanding specific capacitances of 197 and 151 F g(-1) at the current densities of 0.5 and 5 A g(-1) in 6.0 mol L-1 KOH aqueous electrolyte, respectively. Furthermore, the sample also displays more superior rate capacity, which can possess high specific capacitance retention of 77% and 70% at the high current densities of 5 and 40 A g(-1), respectively. In addition, a capacity fading lower than 2% after 5000 cycles of charging and discharging is obtained, indicating its long-term electrochemical stability. (C) 2014 Elsevier Ltd. All rights reserved.