In this work, the different effects of organic montmorillonite (OMMT) particles and shear flow on the crystallization behavior of isotactic polypropylene (iPP) were discussed. While neat iPP and OMMT filled iPP were treated using the multistage stretching extrusion technology, changing the number of laminating-multiplying elements (LMEs) can obtain samples with different dispersion degree of OMMT particles and different orientation degree of molecular chains. With the increase of LME number, the content of beta-crystal in neat iPP increased. But for OMMT/iPP composites, decreasing LME number caused the increase of content of beta-crystal. The experimental results showed that the shear flow and large OMMT aggregations were essential factors for the formation of beta-crystal in composites, and the crystalline morphology strongly depended on the size of OMMT particles. The scanning electron microscope (SEM) images of sample with 3 wt% of OMMT particles and without LME illustrated that beta-transcrystallinity, fan-shaped beta-crystal and alpha-spherulite were induced by different size of OMMT particles, respectively. A schematic was proposed to describe the formation mechanism of alpha-crystal and beta-crystal under the coexistence of OMMT particles and shear flow. (C) 2015 Elsevier Ltd. All rights reserved.