Polyaniline nanostructures with tubular, spherical, polyhedral, dendritic and belt-like morphologies were synthesized by simply tuning the preparation conditions in a two-phase medium. SEM, FTIR and UV-vis were applied for the characterization of the products. The results showed that the polarity of the organic solvents, the amount of ammonium peroxydisulfate (APS) and the concentration of the acetic acid influenced the morphologies of the polyaniline nanostructures. The difference in the polyaniline morphologies was attributed to the difference in the relative rate of interfacial nucleation to aqueous nucleation. The route reported here is expected to be applied for the controlled synthesis of various polymer nanostructures. (c) 2007 Elsevier Ltd. All rights reserved.