Three microstructures of polypropylene (PP)/elastomer/filler hybrids were obtained by processing control and elastomer or PP surface modification : (a) filler and elastomer particles are dispersed in a PP matrix to form separate particles; (b) elastomer particles with a filler core are distributed in a PP matrix; or (c) there are mixed microstructures of (a) and (b). Morphologies and fracture of different components and microstructures were studied by SEM. When the lower-temperature cut samples were carefully etched, the differences between the various microstructures were clearly observed under SEM. The core-shell microstructure provided an elastomer interlayer between the filler and the PP matrix, which resulted in changing the fracture mechanism from microcrack to shear yield. The SEM micrographs were digitized and analyzed by IMAGE 1.52. Rubber particle size and distribution were studied. The relationship between the morphologies and mechanical properties, especially the brittle-toughness transition, was discussed. DSC was used to confirm the difference of microstructures, crystallization behavior, and compatibility.