The effect of inorganic silica nanoparticles on the morphology and viscoelastic properties of polypropylene/poly(ethylene-co-vinyl acetate) (PP/EVA) immiscible blends has been investigated. Different EVA with different molar masses were used in this study. Virgin and filled blends were prepared by using a twin-screw mini-extruder. Microscopy studies revealed a significant change in morphology of PP/EVA blend in the presence of silica nanoparticles. Also, the images proved the migration of silica nanoparticles toward EVA phase, and to the interface. The quantitative analysis of the rheological experimental data was based on the framework of the Palierne model, extended to filled immiscible blends. Based on this model, a method of determination of the interfacial tension from theological measurement has been addressed with an improved accuracy. Even if silica mainly plays a thermodynamic role in the stabilization mechanism by decreasing the effective interfacial tension, the influence of particular theological conditions and the structure of the phases must be taken into account for a complete understanding of the final morphology of such systems. (c) 2008 Elsevier Ltd. All rights reserved.