Porous electrically conducting carbon nanofibers with MnO2 (P-Pitch-PM-Mn) are prepared by electrospinning blended solutions of pitch, poly(methyl methacrylate) (PMMA), manganese(II) chloride (MnCl2), and polyacrylonitrile (PAN) in N,N-dimethylformamide (DMF), and their electrochemical properties are investigated as supercapacitor electrodes. In these nanofiber composites, the pitch plays a key role in developing the surface area and electrical conductivity, whereas the mesopore volume fraction is increased with PMMA addition. These characteristics afford the P-Pitch-PM-Mn composite with the best electrochemical performance as a material for supercapacitor electrodes with a maximum specific capacitance of 183 F g(-1) at 1 mA cm(-2), high energy densities of 25-20 W h kg(-1) in the power density range of 400 to 10,000 W kg(-1), and good rate capability in aqueous solution. Thus, the combination of large specific surface area, high conductivity, and suitable mesoporosity induced by pitch and PMMA improves the electrochemical performance of the P-Pitch-PM-Mn electrodes through the effective charge accumulation at the electrode/electrolyte double-layer interfaces and rapid pathways for electrolyte transportation.