Uniform polyaniline (PANI) nanofibers (average diameter about 30nm) are readily synthesized via a mediated-polymerization method in an aqueous medium by the use of cyclodextrin (CD) to control the secondary growth. Oligomers formed at an early stage act as seeds for the formation of the fully grown PAN! nanofibers. The nucleation-growth theory - "birth-and-spread growth" mechanism - is employed to provide insight into the important effect of CD on the formation of PANI nanofibers. This mediated-polymerization method is able to produce high quality nanofibers in bulk. (C) 2012 Elsevier B.V. All rights reserved.