Nanocomposites of a new type have been prepared containing a constant amount, 4.8 wt%, of montmorillonite (MMT) in a polypropylene (PP) matrix and different amounts of conducting polypyrrole (PPy) varying from 4.8 to 16.7 wt%. For comparison, polypropylene/ polypyrrole (PP/PPy) composites and MMT/PPy nanocomposites with the same composition ratio were synthesized. All polypropylene-containing composites were synthesized in an aqueous solution of the anionic surfactant dodecylbenzenesulfonic acid (DBSA) or in water/methanol. Chemical oxidative polymerization of pyrrole was used for suspension modification of powdered PP, MMT, or mixtures of PP and MMT particles using ferric chloride as oxidant. To investigate the influence of the primary MMT particle structure on conductivity, three types of sodium MMT were used for the preparation of MMT/PPy nanocomposites. Wide angle X-ray scattering (WAXS) studies confirmed the intercalation of conducting PPy into MMT layers. The amount of PPy influences the final conductivity of the composites and nanocomposites. The nanocomposite (PP/4.8 wt% MMT)/PPy containing 16.7 wt% PPy reaches a conductivity of 4.8 x 10(-2) S cm(-1), i.e. more than one order of magnitude higher than the conductivity of the clay-free composite, PP/16.7 wt% PPy prepared as a suspension in water containing the same anionic surfactant, dodecylbenzenesulfonic acid. Thermogravimetric analysis (TGA) proved that the presence of PPy increases the thermal stability of PP/PPy composites as well as (PP/4.8 wt% MMT)/PPy nanocomposites.