Electrochemical capacitors based on hierarchical porous activated carbon nanofiber (RuO₂ / ACNF) composites are fabricated by one-step electrospinning, and then stabilized at different activation temperatures. The effect of activation temperature on the structural properties and electrochemical behavior of the RuO₂ / ACNF composites is intensively investigated in 6M KOH electrolyte .The RuO₂ / ACNF-800 composites activated at high temperature possess abundant mesopores and larger pores, which improve the electrochemical performance, especially at fast charge-discharge rates. The energy storage capabilities of the RuO₂ / ACNF-800 electrode prepared at high temperature areas follows: maximum specific capacitance of 150 Fg-1 and an energy density of 14-20 Whkg-1 in the respective power density range of 400 to 10,000 Wkg-1 in aqueous solution. Furthermore, this electrode exhibits high-rate electrochemical performance with a specific capacitance reduction of less than 28 % of the initial value at a discharge current of 20 mAcm-2. Therefore, the hierarchical porous RuO₂ / ACNF composites with well-developed mesoporous structure provide low resistance for charge diffusion and a short pathway for ion transportation, yielding good capacitive behavior.