The beta-cyclodextrin (beta-CD) and gamma-cyclodextrin (gamma-CD) inclusion complexes (ICs) with four kinds of polyolefin were prepared. The crystallization behavior of isotactic poly(1-butene) (iPB-1) blended with these CDs and ICs was investigated by differential scanning calorimetry, polarized optical microscopy, and wide-angle X-ray diffraction. The iPB-1 blended with the ICs was found to exhibit higher crystallization temperature (T-C), smaller spherulites, and faster crystallization rate than neat iPB-1. These results indicate that the ICs can act as nucleating agent on the crystallization of iPB-1 and induce the accelerated crystallization. The guest molecules of ICs play an important role in the nucleation effect of ICs on the crystallization of iPB-1. ICs with polyolefin having higher T-C as guest molecules have higher nucleation effect than the one with polyolefin having lower T-C as guest molecules. And, the CDs and ICs induce different crystal form of iPB-1. The crystal of iPB-1 blended with CDs is defective, whereas the crystal of iPB-1 blended with ICs is more perfect. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 389-395, 2010