The morphology and mechanical behavior of isotactic polypropylene (iPP) and Noryl blends were studied. It is found that the fracture toughness of iPP can be significantly improved by adding rigid Noryl without causing any reduction in modulus. Large Noryl particles (about 10-15 mu m) are formed if no compatibilizers are utilized in the iPP/Noryl blend. The addition of a small amount of styrene-ethylene-propylene (SEP) compatibilizer causes a significant reduction in Noryl particle size. A noticeable improvement in particle-matrix interfacial adhesion is also observed. Also, the energies required for both crack initiation and crack propagation of iPP are greatly increased. The results show that phase morphology has a great effect on the mechanical performance of these blends. The structure-property relationship in iPP/Noryl blends is discussed in detail. (C) 2000 Elsevier Science Ltd. All rights reserved.