The interfacial property between graphite/epoxy laminate and multi-walled carbon nanotubes (MWNTs)/polymer nanocomposites was investigated. For the graphite/epoxy laminate, the fiber orientations were varied. For the MWNTs/polymer nanocomposites, the epoxy resins were used as the matrix material and the MWNTs were used as the reinforcement. The weight percentage of MWNTs in the MWNTs/polymer nanocomposites beam specimen was varied. The graphite/epoxy laminate and the MWNTs/polymer nanocomposite beam were glued together by epoxy to make the test specimens. To determine the interfacial property, the end notch flexure (ENF) method was used, and the specimen was placed in a three-point bending test to evaluate the critical strain energy release rate Gc. In analysis, the finite element method was used to obtain the numerical values of the critical strain energy release rate Gc and compared with the experimental ones.