Isotactic polypropylene/ organoclay nanocomposites were prepared by a solution methodology and characterized by structural, morphological, and mechanical analysis. X-ray and microscopic analyses (SEM) have revealed a homogeneous dispersion of the nanoclay in the iPP matrix and good adhesion between the two phases, especially in nanocomposites containing lower organoclay amounts ( 1% and 3%). Particularly it was observed that the sample with 1% clay content maintains the exfoliated structure during processing, while the sample with 3% clay evolves from an intercalated structure toward an exfoliated structure when processed by compression molding. The influence of the modified organoclay nanoparticles on the iPP crystallization process was also investigated. The results have shown that while the nanoparticles increase the rate of crystallization there is a delay in the onset of the solidification process. A regime II-III transition temperature was also observed which decreases with increasing organoclay content. © 2005 Wiley Periodicals, Inc.