X-ray diffraction and differential scanning calorimeter (DSC) methods have been used to investigate the crystallization behavior and crystalline structure of hexamethylenediamine (HMDA)-modified maleic-anhydride-grafted polypropylene/clay (PP-g-MA/clay) nanocomposites. These nanocomposites have been prepared by using HMDA to graft the PP-g-MA (designated as PP-g-HMA) and then mixing the PP-g-HMA polymer in hot xylene solution, with the organically modified montmorillonite. Both X-ray diffraction data and transmission electron microscopy images of PP-g-HMA/clay nanocomposites indicate that most of the swellable silicate layers are exfoliated and randomly dispersed into PP-g-HMA matrix. DSC isothermal results revealed that introducing 5 wt % of clay into the PP-g-HMA structure causes strongly heterogeneous nucleation, which induced a change of the crystal growth process from a three-dimensional crystal growth to a two-dimensional spherulitic growth. Mechanical properties of PP-g-HMA/clay nanocomposites performed by dynamic mechanical analysis show significant improvements in the storage modulus when compared to neat PP-g-HMA. (c) 2005 Wiley Periodicals, Inc.