Heterogeneous textures due to phase separation in molten polypropylene (PP)/ethylene–propylene–rubber (EPR) blends were investigated in relation to their dynamic viscoelastic properties. As characteristic to heterogeneous liquids, slow relaxation mechanisms due to the existence of such phases were found for dynamic moduli of PP/EPR blends. These moduli were analyzed by using the linear viscoelastic constitutive equation for an emulsion model developed for the concentrated emulsion and the blending equation for dissimilar polymer system. The results show that the matrix of PP/EPR blends is not pure PP but the mixture of PP and EPR. For the same blend composition, the EPR concentration in the matrix PP phase was larger for EPR containing more propylene units. For the blends having the same EPR, the EPR concentration in the matrix was larger for higher EPR content.