In the area of fiber reinforced composites, several researchers have studied filler incorporated fiber reinforced composites to improve its thermal and mechanical properties. In fabrication of filler incorporated fiber reinforced composite, however, there is challenge in incorporating secondary fillers into fiber bed, which deteriorate ultimate performance of composites. We investigate the mechanism of ultrasonic induced filler migration into fiber bed during solvent impregnation of silica particle incorporated glass fiber reinforced epoxy composite (epoxy/silica prepreg) and its effect on the coefficient of thermal expansion (CTE). The migration of silica particles into glass fiber bed are verified by optical microscope and explained with a theory of ultrasonic cavitation bubble collapse in liquid and liquid-solid system. It is observed that the silica particle migration into glass fiber bed significantly reduce in CTE of epoxy/silica prepreg. We believe that this investigation could show possibility of effective reinforcing in filler incorporated fiber reinforced composites. Keywords: ultrasonication, filler incorporated composites, prepregs, solvent impregnation process, coefficient of thermal expansion (CTE)