Polymer blending is an easy and effective way to obtain new materials with desired properties. However, most polymers are immiscible due to the huge difference in molecular structure. The properties of immiscible polymer blends are highly dependent on the morphology formed during processing. For polymer blends, one of the challenges is that the generated morphologies during processing are usually in a non-equilibrium state. Morphology coarsening, via coalescence, breakup and retraction, was found by a lot of researchers when polymer blends were subjected to thermal annealing in quiescent conditions or second processing, which led to a huge increase in phase size. The effect of nano-silica particles on the morphological evolution of PP/ PS blend is evaluated. The nano-silica particles were found to be selectively dispersed in PS phase. Rheological measurement showed that a particles network structure was formed in the blend when the concentration of the filled nano-silica particles was beyond 6wt%. By using an optical microscope equipped with hot stage, we were able to observe the morphological evolution directly when annealing at melt state. An obvious coalescence of the dispersed droplets was found for the pure blend when annealing in the melt state. With the addition of nano-silica particles, the coalescence was found to be slowed down. For blends filled with 8wt% nano-silica particles, the coalescence was almost stopped. It was showed that the morphology stabilization was closely related to the particles network structure.