Recently, structural adhesives and fiber composites are used in many structural components. Rubber-modified epoxy resins are employed as adhesives and matrix materials for various engineering components. This study focused on the relationship between fracture toughness and damage Brine size around the crack tip of rubber-modified epoxy resin under mixed mode conditions. Fracture toughness(K$_{IC}$) and fracture energy(G$_{c}$) were evaluated using the end notched circle type(ENC) specimens. The damage zone and rubber particles distributed around the crack tip of damaged specimens were also observed on an optical microscope. It is concluded that G$_{c}$ of rubber-modified epoxy resin is closely related to the area of the damage zone. The rubber particles are deformed elliptically due to the difference in principal stresses in the case when the loading angle is 30 degrees.grees.