A series of modified polyisophthalamides were prepared from 5-(phenylamino)carbonyl-1,3-phenylenediamine and 5-benzoylamino-isophthalic acid. The polymers were characterized by FT-IR, H-1-NMR, inherent viscosity, water absorption measurements, x-ray, DTA, TGA, and isothermal gravimetric analysis. The modified polyamides were amorphous and softened at 210-245 degrees C. They showed higher hydrophilicity and better solubility in certain solvents such as DMF, DMSO, CCl3COOH, cyclohexanone, and m-cresol than the corresponding unmodified polyamide. They started to lose weight at 329-344 degrees C in Nz or air, whereas the degradation of unmodified polyamide started at 320 degrees C in N-2 and 308 degrees C in air.