Utilization of woody biomass instead of nonrenewable carbon resources has been attracted considerable attention due to social requirements. Lignins are the most abundant aromatic biomass in nature. Utilization of this abundant biomass has been expected but has not yet been established. One of the practical ways to utilize lignin is to degrade it using the chemical reactions or enzyme reactions of microorganisms to produce utilizable aromatic compounds such as vanillin for aroma or polymer-based chemical. However, these chemical or enzyme reactions concurrently produce various aromatic compounds from lignin not only vanillin and also vanillic acid, syringaldehyde, syringic acid and other mono- or di- aromatic compounds. If we utilize lignin in this way, it is necessary to purify the target compounds from various aromatic compounds mixture. As yet, an efficient system for utilizing lignin has not been established. The soil bacterium, Sphingobium sp. SYK-6, which can degrade various low molecular weight compounds derived from lignin, metabolizes these substances via 2-pyrone-4,6-dicarboxylic acid (PDC). PDC is a final intermediate of lignin biodegradation process, before it was taken into the pyruvate energy cycle. We focused on this metabolic intermediate as a raw material for novel bio-based polymers. This precious dibasic acid can be utilized as a partner molecule of various condensation polymers, since we have succeeded in the massive preparation of PDC by using the transformed bacterial bioreactor system. PDC a chemically stable metabolic intermediate of lignin, was converted into the corresponding acid chloride and thermoplastic polyesters were synthesized by polycondensation with several aromatic diols. The polyesters exhibited high decomposition temperature due to the presence of aromatic group adjacent to the PDC group. The films prepared by hot-pressing gave relatively high fracture stress that is almost comparable to poly(ethylene terephthalate) (PET) and showed oriented crystallization upon stretching.