Self-doping polyaniline (SPANI) nanofibers were synthesized by using self-assembly process consisting of a self-doping monomer (o-aminobenzenesulfonic acid, SAN) and aniline (AN). SAN plays the key roles of a self-doping monomer and a surfactant in the process of forming nanofibers. TEM and SEM results revealed that the morphology, average diameter of the resulting nanofibers depended on the mole ratio of AN to SAN and reaction conditions. NMR, FTIR, XPS, UV-vis spectra were used to describe the molecular structures of the nanofibers. X-ray diffraction was used to characterize the crystallinity in these structures. Results revealed that the molecular structures of polymer chains were similar to those of the emeraldine form of polyaniline (PANI). The doping degree ranged from 21 to 27% corresponding to the AN/SAN mole ratio from 4 to 1. (c) 005 Elsevier Ltd. All rights reserved.