A green route is presented to synthesize bio-based nonisocyanate thermoplastic polyoxamide-ureas (POXAUs) containing flexible poly(propylene oxide) segments. A hexanedioxamide-diester (HDODE) was synthesized from the reaction of 1,6-hexanediamine with excessive diethyl oxalate. Four H2N- terminated polyoxamide prepolymers (PrePOXAs) were synthesized through melt polycondensation of HDODE with O,O'-bis(2-aminopropyl) poly(propylene glycol). Chain extension of PrePOXAs was conducted with bis(hydroxyethyl) hexanediurethane as a chain extender, and four chain-extended POXAs or POXAUs were prepared. The POXAUs were characterized by size exclusion chromatography, Fourier transform infrared, H-1 NMR, wide-angle X-ray scattering, differential scanning calorimetry, thermogravimetric analysis, and tensile testing. POXAUs show M-n up to 29 900 g mol(-1), melting temperature from 148 to 156 degrees C, initial decomposition over 242 degrees C, tensile strength up to 60 MPa, and elongation at break from 8 to 16%. Crystallized bio-based thermoplastic poly(oxamide urea)s with excellent thermal and mechanical properties were successfully synthesized through a nonisocyanate route.