Crystalline structures, nonisothermal crystallization behavior and surface folding free energy of polypropylene (PP)/poly(ethylene-co-vinyl acetate) (EVA) blend-based organically modified montmorillonite (OMMT) nanocomposites were investigated by use of wide angle X-ray scattering (WAXS) and differential scanning calorimetry (DSC) techniques. Nonisothermal crystallization kinetic analysis was performed using Avrami equation modified by Jeziorny as well as combined Avrami-Ozawa method. Surface folding free energy and activation energy for PP and nano-composite samples were also determined employing Hoffman-Lauritzen's and Vyazovkins's approaches, respectively. The results obtained from transmission electron microscopy (TEM) showed that presence of EVA, which attracts most of the layered silicates, reduces number density of heterogeneous nuclei in the matrix and as a consequence, decreases the nucleation rate. Incorporation of EVA, PP-g-MA and OMMT results in a decrease of the chain surface folding free energy level. It was shown that although, OMMT acts as a barrier against the PP macromolecular motion but interestingly, it increases the overall crystallization rate. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 674-684, 2009