This work shows the spectroscopic characterization of polyaniline-montmorillonite clay (PANI-MMT) composites prepared by polymerization of aniline in aqueous suspensions of montmorillonite clay and camphorsulfonic acid containing persulfate ions as oxidizing agent. X-ray diffraction, scanning electron microscopy, and X-ray absorption near Silicon K-edge data show that morphologies and structures of PANI-MMT nanocomposites depend on their relative amount. The electrical conductivity values of composites increase from 10(-4) to 10(-1) S/cm(-1) when PANI-MMT ratio increases, and percolation threshold is observed when polymer/clay mass ratio is changed. Resonance Raman, UV-VIS-NIR spectroscopy, electron spin resonance (EPR) and X-ray absorption near Nitrogen K-edge data confirm that PANI has emeraldine salt form for all PANI-MMT materials prepared. (c) 2006 Elsevier Ltd. All rights reserved.