In this study, bifurfural, an inedible biobased chemical and a second-generation biomass, was polymerized with several diamines using an environmentally benign process, and the chemical structures of the resulting poly(Schiff base)s were analyzed. Because furan rings, which are only produced from biomass and not from fossil resources, endow polymers with unique properties that include high rigidity and expanded π-conjugation, bifurfural, which contains two furan rings, is of significant interest as a biobased building block. 1H NMR, IR, and matrix assisted laser desorption ionization-time of flight mass spectra of the poly(Schiff base)s reveal that they are composed of mixtures of linear and cyclic structures. The UV-vis spectroscopy and molecular orbital theory confirm the extended π-conjugation in the bifurfural/p-phenylenediamine poly(Schiff base) system. Poly(Schiff base)s composed of bifurfural and 1,3-propanediamine, 1,4-butandiamine, 1,5-pentanediamine, and 1,6-hexanediamine were molded at 120 °C into films that exhibited good strengths and were tough to bend. These results indicate that bifurfural-based poly(Schiff base)s are promising biobased materials.