The non-isothermal crystallization behaviour of Mg-Al layered double hydroxide (LDH)/polypropylene (PP) nanocomposites prepared by melt-dispersion was investigated through differential scanning calorimetry and discussed in comparison with that of montmorillonite (MMT)/PP ones. Combined effects of the LDH interlamellar modification and blending the PP with maleic anhydride-grafted PP (PP-g-MAH) and maleic anhydride-grafted poly(styrene-co-ethylenebutylene-co-styrene) (SEBS-g-MAH) were analysed. Different approaches were applied to determinate the crystallization kinetic parameters. The nucleation activity parameter indicated that LDH particle resulted active for heterogeneous nucleation of PR Overall: the crystallization rare constant of the PP increased in presence of LDH in a similar extension that in presence of MMT nanoparticles. By applying an isoconversional method to the calorimetric data it was found that the effective activation energy decreased because of the effect of the nanoparticles and its value displayed different growing trends with the crystallization degree depending of the nanocomposite composition. (c) 2008 Elsevier B.V. All rights reserved.