In this study, melting and isothermal crystallization behaviors of polypropylene (PP) nucleated with different nucleating agents (NAs) have been comparatively studied. a-phase NA 1,3 : 2,4-bis (3,4-dimethylbenzylidene) sorbitol (DMDBS, Millad 3988), (beta-phase NA aryl amides compound (TMB-5), and their compounds were introduced into PP matrix, respectively. The crystallization and melting characteristics as well as the crystallization structures and morphologies of nucleated PP were studied by differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD), and polarized light microscopy (PLM). As indicated by previous work that a few amounts of a-phase NA (DMDBS) or (I-phase NA (TMB-5) has apparent nucleation effect for PP crystallization. However, the crystallization of PP nucleated with compounding NAs is dependent on the content of each NA. In the sample of PP with 0.1 wt % DMDBS and 0.1 wt % TMB-5, the nucleation efficiency of TMB-5 is much higher than that of DMDBS and PP crystallization is mainly nucleated by TMB-5, and in this condition, p-phase PP is the main crystallization structure. For the sample of PP with 0.2 wt % DMDBS and 0.2 wt % TMB-5, 0.2 wt % DMDBS has higher nucleation efficiency than 0.2 wt %. TMB5, and alpha-phase is the main crystalline structure in this sample. The isothermal crystallization kinetics and crystallization structure have been analyzed in detail in this work. (C) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 111: 1624-1637, 2009