Adducts were synthesized from thiokol and epoxy resin using triethylamine as a catalyst, and their structure and molecular weights were determined. The synthesized adducts, which possessed an epoxide group on their chain as a modifier to enhance the toughness of the epoxy resin, were well dispersed in the epoxy matrix, resulting in the successful manufacture of laminate composites made from glass fiber/epoxy resin (GF/EP). The microstructure and mechanical properties, such as the tensile strength, impact resistance and mode I interlaminar fracture toughness, were investigated and compared with those of the GF/EP system. The addition of the adduct to the epoxy matrix led to an increase in both the mode I interlaminar fracture toughness and IZOD impact resistance of the GF/EP.