This article reports crystallization behaviors of isotactic polypropylene (iPP) with an aryl amide derivative (TMB-5) as beta-form nucleating agent. The effects of nucleating agent concentration, thermal history and assemble morphology of nucleating agent on the crystallization behaviors of iPP were studied by differential scanning calorimetry, X-ray diffraction, and polarized optical microscopy. The results indicated that the TMB-5 concentration should surpass a threshold value to get products rich in beta-iPP. The diverse morphologies of TMB-5 are determined by nucleating agent concentration and crystallization condition. At higher concentrations, the recrystallized TMB-5 aggregates into needle-like structure, which induces mixed polymorphic phases on the lateral surface and large amount of beta modification around the tip. High beta nucleation efficiency was obtained at the lowest studied crystallization temperature, which is desirable for real molding process. TMB-5 prefers to recrystallize from the melt at higher concentration and lower crystallization temperature. The difference in solubility, pertinent to concentration and crystallization temperature, determined the distinct crystallization behaviors of iPP. (C) 2008 Wiley Periodicals, Inc.