New aromatic polyamides and polyimides containing benzimidazole or benzoxazinone pendent groups were prepared from 5-(2-benzimidazole)- or 5-(7-benzoxazinone)-1,3-phenylenediamine. They were characterized by inherent viscosity and water absorption measurements, Fourier transform infra-red, H-1 nuclear magnetic resonance, X-ray, thermomechanical, thermogravimetric and isothermal gravimetric analyses. Their properties were compared with those of the parent polymers derived from 1,3-phenylenediamine. The modified polymers displayed better solubility than the unmodified ones and dissolved in polar aprotic solvents and certain inorganic and organic acids. The polyamides bearing benzimidazole or benzoxazinone pendent groups exhibited higher or lower, respectively, hydrophilicity than the reference polyamide. All modified polymers were amorphous and showed lower glass transition temperatures and thermal stability than the corresponding unmodified ones. Some of them softened in the region of 133-205 degrees C.