Simple technology (i.e. one-step polymerization of anilinium sulfate in the presence of montmorillonite) has been used to prepare polyaniline/montmorillonite (PANI/MMT) nanocomposite thin films. The present work is focused on the effect of MMT content on the thickness, morphology and electrical conductivity of PANI/MMT nanocomposite films. An increase in MMT content led to an increase in film thickness and surface roughness and to a decrease in conductivity from a maximum value of 356 S/m to a minimum value of 76 S/m, while for pure PANI films, prepared using the same polymerization procedure (from anilinium sulfate), the conductivity was 59 S/m. On the other hand, the MMT content exhibited a significant impact on the optical transparency of PANI/MMT nanocomposite films, which was limited to the range of 450-650 nm in contrast with pure PANI films showing non-zero transparency in the whole measured range of wave length 300-800 nm. Atomic force microscopy clearly proved the alignment of PANI chains in nanocomposite films in comparison with pure PANI films. Scanning electron microscopy revealed in detail the significant difference in surface morphology between pure PANI films and PANI nanofilms covering the MMT particles. (C) 2014 Elsevier B.V. All rights reserved.