This paper presents the works done to synthesize fully exfoliated polyaniline-clay nanocomposites (PCNs) with high purity via in situ polymerization of aniline in Cloisite 30B nano-clay suspension in supercritical CO2 (ScCO2) medium. The Cloisite 30B was first delaminated with ScCO2 treatment in the presence of aniline monomers. Ammonium peroxydisulfate CAPS) solution was added rapidly into the mixture of delaminated Cloisite 30B and aniline monomers to produce PCNs. Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR). UV-vis spectroscopy and XRD analysis have been used to characterize the morphology and structure of the as-synthesized product. SEM results reveal that nano-clays are fully exfoliated in the final nanocomposite which is synthesized in ScCO2. MR and UV-vis analysis showed that the resulted polyaniline (PAN!) had been in highly conductive emeraldine salt state and ScCO2 does not have any effect on chemical structures of the PANI. (C) 2011 Elsevier B.V. All rights reserved.