An ion-exchange method was applied to replace sodium cations inside the interlamellar space of montmorillonite with positively charged stearyl trimethyl ammonium chloride. The d(001)-spacing of montmorillonite is larger in toluene than in other solvents. The overexchanged stearyl methyl ammonium chloride in the montmorillonite layers can be completely washed out by ethanol. Polypropylene-montmorillonite nanocomposites were prepared by using the supported rac-Et(Ind)(2)ZrCl2 catalyst on the montmorillonite. The nanocomposites that were polymerized by the supported catalyst were characterized by infrared spectroscopy, nuclear magnetic resonance, X-ray diffraction, differential scanning calorimetry, scanning electron microscopy, and transmission electron microscopy. Transmission electron microcopy shows that each silicate sheet of montmorillonite is randomly dispersed into the polypropylene matrix following polymerization by using a supported catalyst. The polypropylene nanocomposites had higher crystallinity, hardness, and thermal properties than pure polypropylene. (C) 2005 Wiley Periodicals, Inc.