The effect of heat treatment of graphite felt (GF) electrode on the performance of aqueous redox flow batteries (ARFBs) using Ferrocyanide and iron-3-[Bis(2-hydroxyethyl)amino]-2-hydroxy-propanesulfonic acid complex (Fe(DIPSO)) as redox couple was evaluated. For the heat treatment of GF, temperature and retention time were determined as main parameters to affect the performance of ARFB. With their changes, the double layer capacitance (DLC) and surface area of GF electrodes were varied. When GF was heat treated at 600 ℃ for 1 h, its DLC and surface area were best as 0.3708 F g-1 and 1.8408m2 g-1. With the enhancements in DLC and surface area, the redox reactivity of Ferrocyanide and Fe(DIPSO) also improved, while their charge transfer resistance reduced. When the heat treated GF was used as electrodes, ARFB single cell using Ferrocyanide and Fe(DIPSO) showed better performance than ARFB single cell using pristine GF without heat treatment. For example, with the heat-treated GF, energy efficiency increased from 56 to 63% at a high current density of 200 mA cm-2, and its maximum power density was 14% more improved.