The present study was carried out on the effect of molecular weight and polydispersity of polypropylene (PP) obtained via Ziegler-Natta or metallocene catalysis on the formation of nanocomposites with montmorillonite and mineral and synthetic hectorite. The formation of the nanocomposites was achieved by the melt-mix method. Xray diffraction, transmission electron microscopy, and analysis of mechanical properties showed that, using PP obtained via metallocene catalysis (polydispersity similar to 2), it is possible to achieve improved formation of nanocomposites compared with PP obtained via Ziegler-Natta catalysis (polydispersity similar to 4). It was also found that the molecular weight of the PP affects the tendency toward clay exfoliation and consequently the properties of the nanocomposites. Montmorillonite type clay was evaluated at 1%, 3%, and 5% by weight in the nanocomposite. The nanocomposite with 1 wt % clay was found to have better mechanical properties compared with the nanocomposite containing 3 wt % and 5 wt %. (c) 2006 Wiley Periodicals, Inc.