The effect of glass beads (GB) on morphology of polystyrene (PS)/poly (methyl methacrylate) (PMMA) blends has been studied by scanning electron microscopy (SEM) at different shear rates and during quiescent annealing. For the viscosity ratio of PMMA to PS greater than unity, the dispersed viscous PMMA phase in the blend coalesced during the shear flow or quiescent annealing. However, the domain size of the PMMA phase decreased significantly under shear even though a small amount of GB was added. The PMMA domain size further decreased and the size distribution became narrower with increasing GB content. According to SEM images, the quiescent coalescence of the PMMA phase was effectively inhibited by adding large amounts of GB, and the breakup of PMMA domains in shear flow was greatly favored by the high local shear prevailed between GB. (C) 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 25-35, 2009