While activated carbons are used as electrode materials in commercial supercapacitors, they are not stable under high voltage operation especially at a positive-electrode side, and this limits the working voltage of supercapacitors to about 2.8 V in organic electrolytes. Thus, revealing the specific carbon chemical structures causing the corrosion is of great significance to come up with ideas of avoiding the corrosion reactions and eventually to achieve high energy density by expanding the working voltage. In this work, a variety of carbon materials are analyzed with many characterization techniques such as X-ray diffraction, Raman spectroscopy, N2 adsorption, magnetic susceptibility measurement, and temperature programmed desorption up to 1800 °C, to find out the origin of corrosion reactions in an organic electrolyte. While carbon crystallinity and porosity are not directly related to the positive-electrode corrosion, a good correlation is found between the corrosion charge and the number of carbon edge sites terminated by H and oxygen-functional groups which are decomposed and release CO. It is thus concluded that the H-terminated edge sites, phenol, ether and carbonyl groups are electroactive sites for the carbon materials used in the positive electrode of supercapacitors.