Phase structure of ternary polypropylene/elastomer/calcium carbonate composites has been investigated using scanning electron microscopy, dynamic mechanical analysis and differential scanning calorimetry. Two kinds of phase structure were observed either a separate dispersion of the phases or encapsulation of the filler by elastomer. The composite phase structure was determined mainly by the chemical character of the components and, to a lesser degree, by the mixing sequences of each component. In this study, the use of non-polar ethylene-octene copolymer (EOR) resulted in a composite having separate dispersion of elastomer and filler particles. When a polar ethylene-vinyl acetate (EVA) elastomer was used, an encapsulation structure was formed. This is attributed to the higher affinity of EVA to calcium carbonate. Analysis of the composite structure formed, using the Geometric Mean approach was found to be useful as a qualitative technique.