Highly-thermostable but degradable polyamides have been synthesized by a polycondensation of bio-derived itaconic acid salts with aromatic diamines to form heterocyclic pyrrolidone ring in the polymer backbone. The molecular weight was greater than 33,600 g/mol. Glass transition temperatures, Tg, and 10% weight loss temperatures, T10, ranged 156–242 °C and 370–400 °C, respectively, which were higher than those of conventional bio-based plastics. However their processability was too low to process the fiber as specimens of mechanical tests. We then incorporated an appropriate amount of aliphatic moiety into the aromatic backbones to prepare the high-performance and processable polyamides with Tg over 115 °C and T10 over 355 °C. The processed fibers showed tensile strength and Young's modulus ranged 20–58 MPa and 0.2–2.3 GPa, respectively. The degradation behaviors inside soil and under ultraviolet-irradiation in water were additionally found.