Both nano- and micro-fillers improved fracture toughness of epoxy under quasi-static loading. The quasi-static fracture toughness of nanocomposites was significantly higher than the micro-particle filled epoxies for any given volume fraction. Nanocomposite specimens containing 10% volume fraction filler yielded the greatest enhancement of fracture toughness (by about 78%) compared to the micro-filler counterparts at the same volume percentage.