ABSTRACT: The interface is critical for stress transfer between polymer matrices and nanofillers, and good understanding of this interfacial communication will help in the design of composites with excellent electrical and mechanical performance. To control the interface, copolymers were utilized to achieve an optimum interfacial adhesion. In this work we studied the compatibilizing impact of styrene ethylene/butadiene-styrene (SEBS) and styrene ethylene/propylene (SEPs) block copolymers on the morphology and electrical and rheological properties of immiscible polypropylene: polystyrene (PP:PS/80:20) / 2vol% multiwall carbon nanotube blend nanocomposite. MWCNTs, known to induce co-continuity in PP: PS blends, did not interfere with the copolymer migration to the interface and thus the morphology refinement. The addition of block copolymers was found to significantly increase the viscoelastic property of the polymer blend nanocomposite, as corroborated but rheological techniques. The triblock copolymer (SEBS) with up to 60wt% PS content shows the highest dynamic moduli, as the morphology shows slight co-continuity. The morphology shows that the interaction between the copolymers and PP or PS is stronger than the interaction of the copolymers and MWCNTs. Characterization of the blend nanocomposites was done using Transmission electron microscopy (TEM), which shows the localization of the MWCNT in the minor phase (PS) and some at the interphase of the blend and that the addition of some of the copolymer changes the MWCNT localization, thus the physical interpretations and structure-property relationships were inferred based on qualitative analysis of the microstructure of the blend composite Keywords: polystyrene, polypropylene, carbon nanotube, interfacial interaction, interface,Copolymers