Thermally exfoliated graphite oxide (GO) has been prepared at a low temperature and ambient pressure usually contains flourish oxygen functional groups. We find that complete oxidized graphite can be successfully expanded, as well as partially exfoliated and reduced at a very low temperature about 200 °C and ambient pressure without any supplementary conditions such as high vacuum or under hydrogen environment. The electrochemical properties of supercapacitor electrodes are studied by cyclic voltammetry (CV) and galvanostatic charge/discharge (DC) methods. Supercapacitors are constructed with as-prepared functionalized graphene have good electrochemical performance, with a maximum specific capacitance of 315 F g−1 at the charge/discharge current density of 100 mA g−1 using 1 M KOH electrolyte and a high charge/discharge efficiency of about 97%.