In this context, we studied the morphologies and morphology evolution of one-dimensional polyaniline (PANI) nanostructures during a wet chemical oxidation process via scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis methods. The results showed that the one-dimensional nanostructures of PANI followed a nucleation, agglomeration or self-growing processes, sequentially. Two distinctive morphologies were observed. One was that cylindrical nanotubes derived, most probably, from the self growing of the as-formed bubble-like ribbons. Another one, in comparison, was rectangular nanotubing structures stemmed from, apparently, a self-guided agglomerating or aggregating process of the as-formed primary nanoparticles, as confirmed unambiguously by both SEM and TEM observations. While the diameters of either individual or hyperbranched PANI nanotubes having a smooth surface were in the range of 250-1500 nm, the size of the rectangular nanotubings was ca. 600 nm. (C) 2008 Elsevier B.V. All rights reserved.