Aqueous dispersed conducting polyaniline nanofiber, new electrode material for supercapacitor, is prepared employing acidic phosphate ester as dopant for nanofibrous polyaniline emeraldine base, which is synthesized by polymerization of aniline using ferric nitrate as oxidant through pseudo-high dilution technique. Highly crystalline and uniform polyaniline fibers with thin diameter of 17-26 nm are obtained, the film from which shows electrical conductivity of 32 S cm(-1). The thin nanofibrous polyaniline is used as electrode material for supercapacitor and its performance is evaluated in non-protonic solvent system. It shows a specific capacitance as high as 160 F g(-1) at discharge rate of 0.4 A g(-1) from -1V to 1 V in 1 mol L(-1) tetraethylammonium tetrafluoroborate/propylene carbonate solution, and the discharge/charge efficiency reaches 92%, indicating that it possesses good electrochemical reversibility. The high capacitance can be attributed to its relatively high surface area of 70 m(2) g(-1), which is 3-5 times higher than spherical polyaniline or thick fiberous polyaniline, leading to high utilization of the electroactive materials. (C) 2011 Elsevier B.V. All rights reserved.