To obtain a biodegradable polymer material with satisfactory thermal properties, higher elongation and modulus of elasticity, a series of biodegradable aliphatic/aromatic co-polyesters, poly(hexylene terephthalate-co-lactide) (PHTL), was synthesized via melt polycondensation from dimethyl terephthalate (DMT), 1,6-hexanediol (HDO) and oligo(lactic acid) (OLA) in the presence of titanium (IV) butoxide. The resulting co-polyesters were characterized by proton nuclear magnetic resonance ((1)H-NMR), differential scanning calorimetry, thermogravimetry and wide-angle X-ray scattering, and their melting temperature, melting heat of fusion, glass-transition temperature (T(g)) and thermal decomposition temperature (T(m)) (1.5 wt%) were obtained. Only one T(g) and two T(m) values were observed for all samples, and were found to decrease gradually with increase of lactide moieties. By using the relative integral areas of the dyad peaks in the (1)H-NMR spectrum of co-polyesters PHTL, the sequence lengths of the hexylene terephthalate (n(HT)) units in the resultant co-polyesters are 3.5. The PHTL co-polyesters exhibited a pronounced hydrolytic degradability, which increase with the content in lactide units. (1)H-NMR analysis of the residue left by evaporation of the mother solution after hydrolytic degradation revealed that the degradation products consisted mostly of lactide and hexylene terephthalate blocks.