A novel electrode material for supercapacitor composed of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT) and graphitic-phase C3N4 (g-C3N4) was prepared by a layer-by-layer assembly method. The resulting composite of PEDOT/g-C3N4 represented excellent electrochemical stability in neutral electrolyte and enhanced electrochemical performance of capacitance and average energy density in comparison with single PEDOT. The specific capacitance was 137Fg−1 in H2SO4 and 200Fg−1 in Na2SO4 at a current density of 2Ag−1, respectively. More significantly, the average energy density was 9.65Whkg−1 at an average power density of 4001.86Wkg−1 in H2SO4. While in Na2SO4, the average energy density reached 17.5Whkg−1 at an average power density of 5000Wkg−1. More than 89% and 96.5% of capacitance were retained in H2SO4 and Na2SO4 respectively, suggesting that PEDOT/g-C3N4 possessed an excellent cycling stability in view of capacity performance as electrode materials. The property improvement was attributed to the synergistic effects of the two components in the composite.