The toughening of the diglycidyl ether of bisphenol A epoxy resin with isocyanate-terminated polyethers(ITPE)was investigated.The progress of the reaction and the structural changes during modification process were studied using FTIR spectroscopy.The studies support the proposition that TDI(tolylene diisocyanate)acts as a coupling agent between the epoxy and polyethers,forming a urethane linkage with the former and the latter,respectively.Me THPA-cured ER/ITPs blends were characterized using dynamic mechanical analysis(DMA)and thermogravimetric analysis(TGA).It is indicated the glass transition temperature(T g )of systems was lower than the T g of pure epoxy resin and overfull ITPE separated from the modified epoxy resin and formed another phase at an ITPE-content of more than 10wt%.The thermal stability was decreased by the introduction of ITPE.The impact strength and the flexural strength of the cured modified-epoxy increased with increasing the ITPE content and a maximum plateau value of about 24.03 kJ/m2 and 130.56 MPa was measured in 10wt%ITPE.From scanning electron microscopy(SEM)studies of the fractrue surfaces of ER/ITPE systems,the nature of the micromechanisms responsible for the increases in toughness of the systems was identified. The toughening of the diglycidyl ether of bisphenol A epoxy resin with isocyanate-terminated polyethers (ITPE) was investigated. The progress of the reaction and the structural changes during modification process were studied using FTIR spectroscopy. Studies of the proposition that TDI (tolylene diisocyanate ) acts as a coupling agent between the epoxy and polyethers, forming a urethane linkage with the former and the latter, respectively. Me THPA-cured ER / ITPs blends were characterized using dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA) is indicated the glass transition temperature (T g) of systems was lower than the T g of pure epoxy resin and overfull ITPE separated from the modified epoxy resin and formed another phase at an ITPE-content of more than 10 wt%. thermal stability was decreased by the introduction of ITPE. The impact strength and the flexural strength of the cured modified-epoxy increased with increasing the ITPE content and a maximum plateau val ue of about 24.03 kJ / m 2 and 130.56 MPa was measured in 10 wt% ITPE. Femme scanning electron microscopy (SEM) studies of the fractrue surfaces of ER / ITPE systems, the nature of the micromechanisms responsible for the increases in toughness of the systems was identified.