Polypropylene (PP) composites containing 0-30 vol% of talc filler, in addition to blends modified with an ethylene-propylene copolymer (EPR) elastomer were prepared and their fracture resistance was determined by the standard Izod impact test and by a fracture mechanics technique. Effects of composition, type of modification, specimen size, and temperature were studied. The validity of linear elastic fracture mechanics (LEFM) conditions were checked : It was shown that under the conditions applied, they can be satisfied even with specimens of reasonable size (4 x 10 x 80 mm) prepared by conventional processing techniques. Calculations of minimum specimen thickness must be carried out, with material properties obtained under the conditions of impact. For heterogeneous blends and composites yield stress should be corrected for the effect of decreasing load-bearing cross section. Linearity of the fracture energy (U) vs. BD phi or U vs. B(D - alpha) plots is not a proof for either elastic or plastic fracture. The composition dependence of fracture properties proved to be practically independent of specimen size, temperature, or measurement technique.