Some polymers can be toughened by rigid inorganic fillers. In this study, the effect of inherent matrix toughness on the fracture of filled thermosets is systematically investigated using glass heads and epoxies. The toughening effect of glass beads, i.e. the relative increase of toughness due to the incorporation of glass beads, follows an increase in the molecular weight of epoxides. Inherent matrix toughness is found to increase with the increase of the epoxide molecular weight, Microscopy studies reveal that the sizes of debonding and micro-shear banding zones are increased as the fracture toughness of composites increases. Matrix shear yielding is identified as one of the major energy absorbing mechanisms fur unmodified and modified epoxies.