The effect of nano-silica particles on the shape relaxation of dispersed droplets in polypropylene/polystyrene (PP/PS) blend was investigated. The nano-silica particles were controlled to be distributed in PS phase, which presented dispersed droplets in the blends. By using an optical microscope equipped with a camera and a hot stage, the shape relaxation of the deformed droplets in the blends after application of a big strain was observed in melt state. The shape relaxation process of PS droplets from highly elongated fibers towards spheres was observed. The nano-silica particles were found to retard the relaxation process of the deformed PS droplets, especially when a particle network was formed. It was showed that the shape relaxation of the droplets was essentially related to the movement of the molecular chains and the relaxation of the oriented chains. These results provide a new understanding of the evolution of morphology for nanoparticles filled polymer blends, based on the slow movement of molecular chains.