In this article, we discuss the crystallization behavior and crystallization kinetics of isotactic polypropylene (iPP) modified by long-chain-branching (LCB) high-melt-strength iPP over a wide composition range, that is, LCB-iPP from 10 to 50 wt %. Over the entire range we investigated, the presence of LCB-iPP accelerated crystallization in both the isothermal crystallization process and nonisothermal crystallization process, even when the LCB-iPP content was as low as 10%, and both crystallization processes were enhanced more significantly as the LCB-iPP content increased. Hoffman-Lauritzen theory analysis revealed that the fold-free energy decreased effectively with the occurrence of the LCB structure, although the growth rate of spherulites was depressed, as shown by polarized optical microscopy. Meanwhile, the regime III-regime 11 transition temperature was about 15 degrees higher for all of the LCB-iPP compositions than that of iPP because the LCB structure reduced the mobility of the polypropylene chains. Furthermore, the gamma-form crystal structure was favored by LCB compared to the beta form, which was Supported by wide-angle X-ray diffraction. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 114: 2180-2194, 2009