Polypropylene (PP) blends with three kinds of grafted macromolecules, PP/Mg(OH)(2) composites and its composites modified by different compatibilizers were prepared by melt extrusion in a twin screw extruder. The crystallization and melting behaviors of PP blends and PP/Mg(OH)2 composites were investigated with differential scanning calorimeter (DSC). The results indicated that addition of PP-g-MA has no influence on the crystallization temperature of PP, but POE-g-MA and EVA-g-MA decrease the crystallization temperature of PP. For PP/Mg(OH)2 composites, addition of Mg(OH)2 increases the crystallization temperature of PP and induces the formation of P-crystal in PP matrix. For PP/Mg(OH)2 composites modified by different compatibilizers, the synergism effect of heterogeneous nucleation of Mg(OH)2 and PP-g-MA or POE-g-MA further increases the crystallization temperatures. For PP/Mg(OH)2 composites modified by EVA-g-MA, the addition of EVA-g-MA to PP/Mg(OH)2 composite has little effect on the crystallization and melting behavior of PP. It is suggested the synergism effect of heterogeneous nucleation of Mg(OH)2 and compatibilizer depends upon the compatibilization between PP and compatibilizer. The increase in crystallization temperatures of PP in PP/Mg(OH)(2)/compatibilizer facilitates the formation of alpha-PP, but weakens the formation of beta-PP. (C) 2007 Elsevier B.V. All rights reserved.