We have investigated the influence of hard spherical hydrophilic nanoparticles (fumed silica) on the phase behavior of PS/PVME (polystyrene/polyvinyl methyl ether) blend as a compatibilizer. The size of nanoparticles is comparable to the radius of gyration of the polymers and the particles preferentially segregate into one of the polymeric components. Phase separation was assessed using theological analysis (RMS), differential scanning calorimetry (DSC), and optical microscopy (OM). In order to investigate the kinetics of phase separation in the presence of nanoparticles, time sweep experiments were employed via theological analysis and OM. A certain composition of PS/PVME was highly concerned to shed light on the dynamic of phase separation, in the presence of nanoparticles, in the unstable region of phase diagram. The phase diagram shifted up nearly 10 degrees C in the presence of nanoparticles. Blends compatibilized by spherical nanoparticles could provide an interesting and economic alternative to the conventional methods of compatibilization by block copolymers.