Toughened epoxy resins were prepared by dissolving poly(ether imide) (PEI) in the EPON HPT 1071 based resin with EPON HPT 1061M as a curing agent. Open tension tests showed an increase in fracture toughness with PEI content, from 0.61 GPa m(1/2) in the pristine resin to 1.32 GPa m(1/2) at 15 wt% PEI. Similar results were obtained for the flexural properties of the epoxy resin. In order to improve the fracture toughness of epoxy resins, increasing the interfacial adhesion strength between the dispersed PEI phase and tetrafunctional epoxy resin was necessary. Improved interfacial adhesion of the modified epoxy resin was obtained through the hydrolysis of PEI. At a concentration of 5 wt% PET, hydrolysed PEI/epoxy resin had 40% more fracture toughness than the unhydrolysed PEI/epoxy resin. The effect of PEI hydrolysis on the flexural properties of the cured epoxy resins was also studied. Scanning electron microscopy was used to investigate the relationship between the morphological study of the fractured epoxy resins and mechanical properties of the modified epoxy resins.