Morphology control in immiscible polymer blends is a key issue in tuning their macroscopic properties. The final microstructural state of these materials is largely dependent on the extent of phase coalescence during processing. In this regard, stabilizing the morphology of an immiscible blend via incorporating solid particles can be considered as a cost effective alternative to conventional compatibilization techniques such as the addition of chemically synthesized compatibilizers. The objective of this study is to shed light on the influence of nanoparticles on the rheological behavior and morphology of immiscible polymer blends consisting of a polypropylene (PP) and an ethylene octene copolymer (EOC) in the 75/25 (PP/EOC) weight ratio with different contents of nanosilica. Maleic anhydride grafted species of PP and EOC were also used to favor the localization of the silica particles in the matrix or dispersed phase, respectively. Although the presence of silica particles resulted in an improved morphological stability of all nanocomposites, the effect was found to be significantly more pronounced when the solid inclusions were localized in the dispersed EOC phase; these composites featured finer microstructures with interfacial area up to 5 times larger and dramatically enhanced dynamic viscoelastic properties. The low frequency data of these systems were predicted using a generalized Maxwell model for which the parameters were determined based on the dynamic frequency sweep data as well as using an extended set of transient creep data reflecting the long time relaxation behavior. The high concentration silica nanocomposite was shown to exhibit three crossover frequencies. Such a behavior was attributed to different relaxation mechanisms corresponding to the interfacial elasticity of the immiscible polymers and the formation of networks of dispersed droplets and solid particles as observed by microscopy.