One-dimensional nanostructures of polyaniline (PANI) doped with (1S)-(+)-10-camphorsulfonic acid (D-CSA) alone and with NiCl2 as a codopant were synthesized via in situ polymerization. PANI nanofibers with diameters of about 200 nm were formed when PANI was doped with D-CSA only. When NiCl2 was added as a codopant, the morphology of PANI obviously changed. The effects and related mechanisms were investigated by Fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy, inductively coupled plasma-atomic emission spectroscopy, and X-ray diffraction, and the results indicated that Ni2+ destroyed the micelles' structure by chemical conjunction with -SO3H groups in camphorsulfonic acid (CSA) molecules, which were the key component in forming the CSA-aniline micelles. The combination between Ni2+ and SO3- in CSA with a lower addition of Ni2+ led to a reduction of CSA doping to PANI, but a higher loading of Ni2+ brought about the direct doping of Ni2+ to PANI, which caused a higher degree of doping and oxidation. The conductivity of PANI increased almost linearly with increasing Ni2+. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 121: 3439-3445, 2011