In order to study systematically the effect of halogen substituents on both the solubility and the thermal stability of aromatic polyamides, new diamine monomers have been synthesized by introducing chlorine groups onto various positions of 4,4'-diaminobenzanilide for the preparation of chlorinated aromatic polyamides. The monochlorinated aromatic polyamides, i.e., P-LCl and P-RCl, exhibited liquid crystalline property in 100% sulfuric acid solution in the temperature range from 40 and 60 degrees C. However, the dichlorinated sample, i.e. P-LRCl, did not exhibit the liquid crystalline property due to the bulkiness of two chlorine groups. Both P-LCl and P-RCl exhibited unimodal decomposition behavior in contrast to the chlorinated poly(p-phenylene terephthalamide) (PPTA) that has been known to show bimodal decomposition behavior. The decomposition onset temperature of both P-LCl and P-RCl was 567 degrees C, which was higher than 549 degrees C of unchlorinated polyamide, P-NCl, but the same as that of PPTA. The char yield was about 50% for both P-LCl and P-RCl and higher than 40% of both PPTA and P-NCl. In the case of P-LRCl, the decomposition onset temperature was 480 degrees C, but the highest char yield of 60% was obtained.