The multiphase morphology of high impact polypropylene (hiPP), which is a reactor blend of polypropylene (PP) with ethylene-propylene copolymer, was investigated by transmission electron microscopy, selected area electron diffraction, atomic force microscopy, and field-emission scanning electron microscopy techniques in conjunction with an analysis of the hiPP composition and chain structure based on solvent fractionation, C-13-NMR, and differential scanning calorimetry measurements. A multilayered core-shell structure of the dispersed phase of hiPP in solution-cast films and the bulk was observed. The inner core was mainly composed of polyethylene (including its long blocks) together with part of PP, the intermediate layer was ethylene-propylene random copolymer, and the outer shell consisted of ethylene-propylene multi-block copolymers. The formation process and controlling factors of the multilayered core-shell structure are discussed. This kind of multiphase morphology of hiPP caused the material to possess both a high rigidity and high toughness. (C) 2008 Wiley Periodicals, Inc.