Many reseachers have investigated fracture properties and various mechanical properties of unidirectional fiber-epoxy resin composites. The interfacial strength between fiber and matrix and the matrix strength are very important factor on the mechanical properties of composite. We observed the effect of GN used as chain extender on DGEBA/MDA matrix strength and the effect of coupling agent treatment on interfacial strength through measuring the fracture energy by three point bending test in DGEBA/MDA/GN(10phr) system. The fracture energy or coupling agent treated carbon fiber was decreased and the fracture energy of this composite was slightly increased as the increment of GN content