High impact polypropylene (HIPP) was prepared by in situ blending of isotactic polypropylene and ethylene-propylene rubber (EPR) with spherical Ziegler-Natta catalyst. Morphology and pore characteristics of such HIPP were investigated by scanning electron microscope, atomic force microscopy, and mercury intrusion. Amorphous phase was removed from polypropylene matrix and characterized by C-13 NMR spectrum. It was found that the EPR prepared in this manner contained variable composition polymer chains with a distribution of ethylene and propylene sequence lengths. Final products of HIPP were free flowing, spherical granules. There were small pores in HIPP, which seemed not to be filled up, and could be determined by mercury intrusion even when the content of rubber was up to 24 wt %. Homopolypropylene with pore diameter between 100 and 10,000 nm was suitable for EPR to fill in during ethylene-propylene copolymerization. The block copolymer fractions act as a compatilizer between matrix and EPR. (c) 2006 Wiley Periodicals, Inc.