The crystallization behavior of olefin block copolymer (OBC) in alpha- and beta-polypropylene (PP) matrix was comparatively investigated. According to the DSC results, the crystallization temperature of OBC (T-cOBC) is 107.9 degrees C, while for various PP blends containing 10 wt% of OBC, these values in alpha- and beta-PP/OBC blends are 113.1 degrees C and 99.2 degrees C, respectively. Unlike the elevated T-cOBC value in alpha-PP/OBC blend, the T-cOBC value in the beta-PP based counterpart is decreased compared to that in neat OBC, indicating inhibited crystallization. Structural investigations revealed that the inhibited crystallization of OBC in beta-PP may be related to the unique crystalline structure of beta-PP matrix. The more loosely arranged interfibrillar region in beta-PP matrix is capable of accommodating OBC hard blocks and inducing finer dispersion of OBC, which may lead to fewer OBC crystallization nuclei in each OBC micro-domain, and consequently the slower crystallization of OBC in beta-PP matrix. (c) 2013 Elsevier Ltd. All rights reserved.