The gamma-cyclodextrin (gamma-CD) inclusion complexes (ICs) with four kinds of polyolefin (PO) as guest molecules were prepared. The crystallization behavior of isotactic polypropylene (iPP) blended with the gamma-CD and gamma-CD-PO ICs was investigated by differential scanning calorimetry, polarized optical microscopy, and light scattering. The iPP blended with the ICs was found to exhibit higher crystallization temperature (T-C), smaller spherulites, and faster crystallization rate than those of neat iPP, indicating that the ICs play a role of nucleating agent on the crystallization of iPP and induce accelerated crystallization. The IC with PO having higher T-C as guest molecules showed higher nucleation effect than the IC with PO having lower T-C as guest molecules. The results suggest that the nucleation effect of these ICs was affected by the kinds of the guest molecules. The higher T-C guest molecules could result in higher nucleation effect. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115: 1098-1104, 2010