We have produced fully biomass-based poly(butylene succinate) (PBS) from furfural produced from inedible agricultural cellulosic waste. Furfural was oxidized to give fumaric acid. Fumaric acid was hydrogenated under high pressure with a palladium-rhenium/carbon catalyst to give 1,4-butanediol, and with a palladium/carbon catalyst to give succinic acid. Dimethyl succinate was synthesized from fumaric acid by esterification and hydrogenation under normal pressure. Fully biomass-based PBS was obtained by polycondensation of biomass-based 1,4-butanediol and biomass-based succinic acid or dimethyl succinate. The biomass carbon ratio calculated from C-14 concentrations measured by accelerator Mass spectroscopy (ANIS) verified that the PBS obtained in this study contained only biomass carbon, The polycondensation of biomass-based 1,4-butanediol and petroleum-based terephthalic acid or dimethyl terephthalate gave partially biomass-based poly(butylene tea:phthalate). which is an engineering plastic.