The morphology of toughened polypropylene with balanced rigidity (TRPP) was characterized by using transmission electron microscopy and polarizing light microscopy. The crystallization behavior and thermal properties were investigated by differential thermal analysis and thermogravimetric analysis. The PP component in the polymer blend was realized as the continuous phase and the elastomer component as the dispersed phase with a cellular structure (salami structure) containing some PP. The particles of the dispersed phase were small and regular. The cellular structure of the TRPPs resulted from the introduction of toughening master batches and was similar to the morphology of acrylonitrile‐butadiene‐styrene and high‐impact polystyrene synthesized by graft copolymerization. By gradually cooling from the melt, crystallization of TRPPs was nucleated heterogeneously and the crystallization temperature was slightly higher than that of PP whereas the crystallite size was remarkably reduced. For the samples with different compositions, the number, shape, and size of the cellular dispersed particles and the crystallite size were different. Considering the toughening theories and our experimental data, it was concluded that the samples with more regular and small cellular dispersed particles generally had better mechanical properties and the remarkably reduced crystallite size of PP was favorable for toughness improvement. The melting point, thermal oxidation temperature, and thermal oxidation onset temperature of the TRPPs were all a little lower than those of PP and the processability remained good. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1351–1358, 2001