The chemical modification of the structure of the unsaturated polyester obtained in poly condensation process of 1,2,3,6-tetrahydrophthalic anhydride, maleic anhydride, and ethylene glycol by well known conventional method of epoxidation with peracetic acid in mild conditions has been presented. The new material containing both epoxy groups and unsaturated double bonds in polyester chain was characterized by FTIR and H-1 NMR spectra. The prepared unsaturated epoxy polyester was suitable material for further chemical modification. Both epoxy groups and unsaturated double bonds can be used as cross-linking sites. Curing behavior, thermal, and visco elastic properties of the unsaturated epoxy polyester cured with different hardeners: 1,2,3,6-tetrahydrophthalic anhydride (THPA), hexahydrophthalic anhydride (HHPA), and/or with vinyl monomer (styrene) using radical initiator-benzoyl peroxide (BPO) were studied by differential scanning calorimetry (DSC), thermo gravimetric analysis (TGA), and dynamic mechanical analysis (DMA). (c) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 110: 3582-3589, 2008