A new aminocarboxylic acid bearing an enamino nitrile segment was used as starting material for the preparation of modified homopolyamide and various copolyamides. The polycondensations were carried out by the phosphorylation method. Poly(benzamide) was also prepared under the same experimental conditions for comparative purposes. Polyamides were characterized by i.r. and JH-NMR spectroscopy as well as by inherent viscosity measurements. The modified polyamides showed higher solubility in common organic solvents than poly(benzamide). Their solubility was increased with increasing concentration of the enamino nitrile segments. Thermal stability of cured (at 300 ° for 15 hr) polyamides was evaluated by TGA and isothermal gravimetric analysis. The modified polyamides displayed higher heat resistance than poly(benzamide) attributable to a rearrangement, at least in part, of the enamino nitrile segments to 4-aminoquinoline. They were stable up to 381-415 ° in N 2 or air and afforded anaerobic char yields of 64-70% at 800 °. Thermal stability of copolyamides was correlated with the concentration of enamino nitrile units.