Polypropylene (PP) and polypropylene/polypropylene-g-maleic anhydride/ organomontmorillonite (PP/PP-g-MA/OMMT) nanocomposites were modified with 0.05 to 0.3% (w/w) of the aryl amide beta-nucleator to promote the formation of hexagonal crystal modification (beta-phase) during melt crystallization. The nonisothermal crystallization behavior of PP, PP/PP-g-MA/OMMT and beta-nucleated PP/PP-g-MA/OMMT nanocomposites were studied by means of differential scanning calorimetry. Structure-property relationships of the PP nanocomposites prepared by melt compounding were mainly focused on the effect and quantity of the aryl amide nucleator. The morphological observations, obtained from scanning electron microscopy, transmission electron microscopy and Xray diffraction analyses are presented in conjunction with the thermal, rheological, and mechanical properties of these nanocomposites. Chemical interactions in the nanocomposites were observed by FT-IR. It was found that the beta-crystal modification affected the thermal and mechanical properties of PP and PP/PP-g-MA/OMMT nanocomposites, while the PP/PP-g-MA/OMMT nanocomposites of the study gained both a higher impact strength (50%) and flexural modulus (30%) compared to that of the neat PP. beta-nucleation of the PP/PP-g-MA/OMMT nanocomposites provided a slight reduction in density and some 207% improvement in the very low tensile elongation at break at 92% beta nucleation. The crystallization peak temperature (T(cp)) of the PP/PP-g-MA/OMMT nanocomposite was slightly higher (116 degrees C) than the neat PP (113 degrees C), whereas the beta-nucleation increased the crystallization temperature of the PP/PP-g-MA/OMMT/aryl amide to 128 degrees C, which is of great advantage in a commercial-scale mold processing of the nanocomposites with the resulting lower cycle times. The beta nucleation of PP nanocomposites can thus be optimized to obtain a better balance between thermal and mechanical properties. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 122: 1066-1076, 2011