For incompletely reduced graphene oxides (RGOs), an effect of oxygen functional groups such as carboxyl, phenol, carbonyl, and quinone on electrochemical capacitive behavior was studied. To prepare RGO thin-film electrodes, a simple fabrication process by (i) dropping and evaporating the graphene oxide (GO) solution, (ii) irradiating pulsed light, and (iii) heat-treating at 200 ∼ 360°C was applied. It was notable that the pulsed light irradiation was effective to prevent the disfiguring of deposited GO thin-film during the thermal reduction. From XRD analyses, interlayer distances of the RGOs were gradually decreased from 0.379 to 0.354nm. As increasing the thermal reduction temperature from 200 to 360°C, XPS O 1s spectra analyses showed that the atomic percentages of carboxyl and phenol of the RGOs were sustained as 5.40±0.36 and 4.77±0.41 at% respectively. Meanwhile, those of carbonyl and quinone of the RGOs were gradually declined from 3.10 to 1.81 and from 1.32 to 0.65 at% with different thermal reduction temperature respectively. For all RGO thin-film electrodes, the specific capacitance from the CV measurement in 6M KOH was sustained as ca. 220 F g−1 at the scan of 5mV s−1. However, in 1M H2SO4, the specific capacitance was gradually decreased from 171 to 136 F g−1. After 100,000 cycles in 6M KOH, 1M H2SO4, and 0.5M Na2SO4, the RGO (200°C) electrodes showed ca. 92, 54, and 104% of the initial capacitances respectively. The atomic percentages of the oxygen functional groups involved in the pseudocapacitive Faradaic reaction were decreased after the cycle test. Especially in 1M H2SO4, quinone group was decreased to ca. 48% of initial atomic percentage, which seems to be a main reason for the drastic reduction of capacitance. The specific pseudocapacitance per unit atomic percentage for either carboxyl or phenol group in 6M KOH was obtained as 12.59 F g−1 at%−1. For carbonyl group in 1M H2SO4, it was a slightly deviated value as 13.55 F g−1 at%−1. For quinone group in 1M H2SO4, it was 27.09 F g−1at%−1.