Abstract: Three kinds of reactive toughening accelerators for epoxy resin/dicyandiamide system, amine-terminated chain-extended urea(TP), imidazole-terminated chain-extended urea(TI₀) and 2-methylimidazole-terminated chain-extended urea (TI₁) were synthesized from polyurethane prepolymer. Compared with the unmodified system, the curing activity, glass transition temperature, impact property and fracture surface morphology of the modified systems were investigated by DSC, SEM and measurement viscoelasticity. The results show that the curing activity was so greatly enhanced that the curing peak temperature decreased from 190℃ for the unmodified system to 120~140℃ for the modified systems, and the apparent activation energy of curing reaction decreased from 131 kJ/mol to 70~80 kJ/mol. Furthermore, the impact strength of the curing systems modified with TI_n was 2~3 times as high as that of the unmodified system, while the glass transition temperature was little changed, and the fracture surface of the modified systems became tougher.