A convenient synthetic route of poly(3HB-co-3HH-co-SEB) terpolyesters has been reported. The developed protocol consists of two steps; poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHx) oligoesterdiols were synthesized via selective reduction of biopolyesters and then via their polycondensation with sebacoyl chloride the biodegradable terpolyesters, poly(3HB-co-3HH-co-SEB), were obtained. The structure of the obtained terpolyesters was established by NMR analysis supported by mass spectrometry. Modification of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) by incorporating units derived from sebacic acid into its chains resulted in terpolyesters with better physico-chemical properties than the starting PHBHx biopolyester. These new polyester materials have greater thermal stability than the starting biopolyester. Furthermore, the introduction of sebacic acid units to a polyester chain leads to the reduction of the glass transition temperatures of the materials and reduces the required processing temperature. A preliminary study confirmed that poly(3HB-co-3HH-co-SEB) terpolyesters can be used to create scaffolds for cell cultures in the form of a three-dimensional spatial structure. Moreover, a toxicity test of the obtained terpolyester carried out on human cells demonstrated that the novel terpolyester is not toxic to human cells in vitro.