Polypropylene and calcium carbonate were prepared by melt extrusion in a twin screw extruder or casting in a kneader extruder. The dispersion of CaCO3 particles in PP was analysed through the observation of impact-fracture surface, polished surface, cross-section surface and film using scanning electron microscopy (SEM), focused ion beam (FIB) and optical transmission microscopy (OTM). Only basic information on particle dispersion was obtained from the investigation of fracture surfaces by SEM and the FIB cross-sections by virtue of the ambiguous phase contrast and the limited area observed. However, the SEM images from polished-surfaces and the film images observed in OTM show the different particle dispersion in different samples. The derived Particle Size Distribution (PSD) curves from OTM images explain the difference of impact strength, demonstrating the relationship between particle dispersion and mechanical properties. (C) 2014 Elsevier Ltd. All rights reserved.