<b>Characterization of Polymer Composite Materials Based on Epoxy Resin GELR 128 Modified with Epoxidized Sunflower Oil Cured by 4.4’ Diaminodiphenylmethane</b> Epoxidized sunflower oil ESO is used to modify the epoxy resin GELR 128 for increase the toughness of epoxy resin. ESO mixed with epoxy resin at different concentrations by one stage and two stage process. Epoxy resin GELR 128 and epoxidized sunflower oil were cured by aromatic amine curing agent 4.4 diaminodiphenylmethane DDM . Morphology, physicochemical, thermal properties of the epoxy resin GELR 128 after denaturation and curing indicated that the two stage process is more better than the one stage process which achieved by amount of ESO content is 15 phr The best tensile strength, flexural strength, impact strength are 66.22 MPa, 81.7 MPa, 32 kJ m2, and maximum decomposition temperature 394.5500C. epoxy resin GELR 128, 4,4 diaminodiphenylmethane, epoxidized sunflower oil, toughness, high temperature curing 52-57 Issue-5 Volume-2 Bach Trong Phuc | Vu Huu Hung