Nanoscaled polyaniline (PANT) fibers with 1730 nm in diameter were successfully prepared by oxidation polymerization using ferric hydrochloride (FeCl3 center dot 6H(2)O) as an oxidant in the presence of p-toluenesulfonic acid (p-TSA), beta-naphthalenesulfonic acid (beta-NSA), and camphorsulfonic acid (CSA) as the dopants. The resulting nanofibers show smaller diameter, higher crystallinity and conductivity (10(-1) S center dot cm(-1)) compared with the nanofibers oxidized by ammonium persulfate (APS), which may be due to the lower oxidation/reduction potential of FeCl3.