In this study, PEL [copolymer of polypropylene) oxide (PPO) and poly(ethylene oxide) (PEO)] toughening epoxy resin with ionic charge was used to produce an interpenetrating action between the cross-linking network structure of the epoxy resin and the PEL additive. Fourier transform infrared (FTIR) analysis of the toughening epoxy resin revealed that -NCO disappeared at 2400 cm(-1), -NH appeared at 3300 cm(-1), and -C==O appeared at 1750 cm(-1). These results indicate that a urethane bond was produced. Dynamic mechanical analysis (DMA) and mechanical testing results indicated that as the level of PEL increased, the compatibility between the epoxy resin and PEL also increased. In addition, the compatibility, was improved because the addition of cornate hardener produced a graft phenomenon. The tensile property, impact strength, and fracture toughness of PEL toughening epoxy resin all had a tendency to improve. The tensile strength, impact strength, and fracture toughness (K-IC value) were most improved when 30 phr cornate was added.