In this research, HDPE/EOC blends containing 10, 20, 40 and 80 Wt. % of EOC, also their Nanocompositses with 5 Wt. % Nano Silica were prepared via melt mixing using a brabender. The Rheology and Morphology of samples were studied using Rheomechanical analysis and Atomic Force Microscopy (AFM). The results showed that HDPE/EOC blends are incompatible and show two phases Morphology in all studied compositions. AFM micrographs showed that in blends containing less amount of EOC (10 and 20 Wt. %), the morphology is matrix dispersed and this result was confirmed by palierne model too. In HDPE/EOC/Nanosilica samples, it was found that the Nanosilica particles are located in EOC phase. The location of nano particles in EOC, leads to increasing the viscosity of this phase, so it will be closer to HDPE viscosity. By approaching the viscosity ratio of HDPE and EOC to 1, the smaller size of EOC phase in PE matrix was obtained. So it is concluded that nanosilica particles can have a compatibilising effect in HDPE/EOC blends. Keywords: Polymer blends, HDPE, EOC,Nanosilica,Nanocomposites