We, in this study, fabricated and applicated MnO2/carbon fiber nanocomposite web as electrode for supercapacitors prepared by co-electrospinning technique. At first, the PAN-Mn3O4 fiber web was prepared by an electrospinning technique to use the mixed solution of both polyacrylonitrile (PAN) in N,N-dimethylformamide (DMF) and 5 ~ 20 wt. % manganese oxide hydrate (Mn3O4). The electrospun PAN-Mn3O4 fiber web was stabilized at 280℃, and then carbon-Mn3O4 nanofiber web was carbonized at 1000℃ in the nitrogen atmosphere. The activated carbon/MnO2 electrospun fiber web was synthesized by activating at 800℃ in steam atmosphere. The structure of manganese oxide was changed that Mn3O4 was changed MnO2 during the carbonization and activation of nanocomposite web. The specific capacitance is increased with increasing Mn3O4 contents was 15 wt.%. But the specific capacitance is decreased at 20 wt.% Mn3O4/carbon nanofiber. The specific capacitances of 5 wt.% Mn3O4/carbon, 10 wt.% Mn3O4/carbon, 15 wt.% Mn3O4/carbon, 20 wt.% Mn3O4/carbon and activated carbon nanofiber or nanofiber composite electrode are 170, 230, 260, 175, 140 F/g, respectively at 1mA/Cm2. In the case of Mn3O4 addition, the specific capacitance is improved due to the synergic effect of pseudocapacitance. But the diameter of carbon fiber increased with the contents of Mn3O4 is increased. So the electro double layer capacitance is decreased.