Biomass plastics are expected to contribute to the establishment of a carbon-neutral society by replacing conventional plastics derived from petroleum. The biomass-derived aromatic amine 4-aminocinnamic acid (4ACA) produced by recombinant bacteria is applied to the synthesis of high-performance biopolymers such as polyamides and polyimides. Here, we developed a microbial catalyst that hydrogenates the alpha,beta-unsaturated carboxylic acid of 4ACA to generate 4-aminohydrocinnamic acid (4AHCA). The ability of 10 microbial genes for enoate and xenobiotic reductases expressed in Escherichia coli to convert 4ACA to 4AHCA was assessed. A strain producing 2-enoate reductase from Clostridium acetobutylicum (ca2ENR) reduced 4ACA to 4AHCA with a yield of > 95% mol mol(-1) and reaction rates of 3.4 +/- 0.4 and 4.4 +/- 0.6 mM h(-1) OD600 (-1) at the optimum pH of 7.0 under aerobic and anaerobic conditions, respectively. This recombinant strain reduced caffeic, cinnamic, coumaric, and 4-nitrocinnamic acids to their corresponding propanoic acid derivatives. We polycondensed 4AHCA generated from biomass-derived 4ACA by dehydration under a catalyst to form high-molecular-weight poly(4AHCA) with a molecular weight of M (n) = 1.94 MDa. This polyamide had high thermal properties as indicated by a 10% reduction in weight at a temperature of T (d10) = 394 A degrees C and a glass transition temperature of T (g) = 240 A degrees C. Poly(4AHCA) derived from biomass is stable at high temperatures and could be applicable to the production of high-performance engineering plastics.