Polypropylene (PP) nanocomposites were prepared by a melting-compounding process with a montmorillonite (MMT) suspension. In this process, an organically modified MMT was swollen in a polar solvent and blended with molten PP in an extruder; this was followed by solvent removal. The effect of a coswelling agent was also evaluated. The nanocomposites were characterized with X-ray diffraction, transmission electron microscopy, differential scanning calorimetry, and scanning electron microscopy. In addition, the mechanical properties of the materials were studied. The nanocomposites prepared with the clay suspension presented a remarkable increase in the impact strength with the maintenance of their flexural modulus. The mechanical properties of the nanocomposites were found to be related to the interaction between PP and the clay. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 121: 389-394, 2011