Abstract: A series biodegradable copolyesters, poly(butylene sebacate-co-terephthalate) (PBSeT), were synthesized by using terephthalic acid (TPA), sebacic acid (SeA) and butylene glycol (BDO) as raw materials through esterification and polycondensation. The effect of molar ratio of SeA and TPA on the structures, thermal, mechanical and degradation properties of PBSeT was studied. The weight average molecular weight of PBSeT was distributed in the range of 178300 to 214277 g/mol. The melt temperature and crystallization temperature of PBSeT decreased at first and then increased with an increase of the content of rigid monomer TPA. PBSeT exhibited the weakest crystallization capacity at the SeA/TPA molar ratio of 50/50. When the TPA content increased from 10 mol.% to 90 mol.%, the glass transition temperature of PBSeT increased gradually. The thermal stabilities of PBSeT copolyesters were relatively similar at different mass ratios. PBSeT also exhibited higher tensile strength at a higher content of TPA, and it reached a maximum value at the SeA/TPA molar ratio of 30/70. However, its elongation at break reached a maximum value of 1040% at the SeA/TPA molar ratio of 50/50. PBSeT presented a typical pseudoplastic fluid, and its complex viscosity, storage modulus and loss modulus increased gradually with an increase of angular frequency. The degradation experimental results of Aspergillus niger indicated that the degradation capability of PBSeT decreased with an increase of the content of TPA monomer.