A new family of aromatic polyamides were prepared from six aromatic diamines and a new monomer derived from isophthalic acid : 5-(2-benzothiazolyl)isophthaloyl chloride. Theoretical calculations of the reactivity of the new monomer were made by semiempirical methods. The polymers were synthesized by the solution polycondensation method at low temperature, in high yields and moderate to high inherent viscosities. The presence of pendent benzothiazole rings brought about remarkable changes in the spectral (nuclear magnetic resonance) characteristics, compared with those of the homologous unmodified polyisophthalamides. Noticeable improvements were observed also for the solubility and for the glass transition temperatures, which rose 20-30-degrees-C relative to those of the conventional polyisophthalamides. Thermogravimetric analyses showed that the new polymers have better thermal stability than the unmodified ones.