Carbon nanofiber paper with high surface area was prepared by surface chemical etching of electrospun phenolic-based nanofiber paper with KOH. KOH was coated on the surface of nanofibers and chemical etching was performed by one-step heat treatment. The specific surface area, pore volume and surface oxygen-containing functionality of the resultant carbon paper are increased significantly with the increase of the KOH uptake on the phenolic-based nanofiber paper. The obtained porous carbon paper have a maximal surface area of 1317 m(2) g(-1), pore volume of 0.699 cm(3) g-1 and surface oxygen species of 15.1 at.%. The carbon paper was used as binder-free electrode for supercapacitor and the electrochemical performance was investigated in aqueous electrolyte (6 M KOH solution) and organic electrolyte (1 M (C2H5)(4)NBF4/PC). Supercapacitor based on this flexible carbon paper high specific capacitance (362 F g(-1)), ultra-high rate handling capacity (209 F g(-1) at 20 A g(-1)) and high energy density (7.1 W h kg(-1) in aqueous electrolyte, 27.9W h kg(-1) in organic electrolyte), which is due to efficient charge accommodation in micropores, considerable pseudocapacitance provided by surface active species and fast ion response derived from short pore channel. These features make the porous carbon nanofiber paper a quite promising alternative for the next generation of high-performance supercapacitors. (C) 2014 Elsevier B.V. All rights reserved.