Mesoporous carbon (MoC), prepared by the template method from phenol resin, commercial mesoporous carbon fiber (ACF) and microporous activated carbon (MiC) were heat-treated under 1200°C in nitrogen. The samples before and after high temperature heat treatment (HTT) were used as electrodes in 30% KOH electrolyte for supercapacitor. The structure and electrochemical properties of these samples were characterized by X-ray diffraction (XRD), galvanotactic charge–discharge, cyclic voltammetry (CV) and electrochemical impedance spectra, respectively. Results showed that HTT caused a remarkable increase of mesoporous ratio in texture accompanied with a significant reduction of surface area. After HTT, the layer–layer space among graphite crystallite decreased and the degree of graphitization was improved. The capacitance values of mesoporous carbons increased and a more stable tendency for specific capacitance was obtained compared with the contrary performance of MiC-1200. The cyclic voltammetry of the samples at different sweep rates was close to the rectangular shape, which represented the lower ESR and higher power density. It was also found that high temperature treatment could improve the electrical conductivity and decrease the impedance of the electrode remarkably. The improved specific capacitance and the better conductivity of mesoporous carbons could be ascribed to the expanding and reorganization of crystallite structure as well as increase of mesopore ratio.