Fifteen highly regular hydrogen-bonded, novel thermotropic, aromatic-aliphatic poly(ester-amide)s (PEAs) were synthesized from aliphatic amido diols by melt polycondensation with dimethyl terephthalate and solution polycondensation with terephthaloyl chloride. Intermolecular hydrogen bonds more or less perpendicular to the main-chain direction induce the formation and stabilization of liquid crystalline property for these PEAs. The structure of these polymers, even in the mesomorphic phase is dominated by hydrogen bonds between the amide-amide and amide-ester groups in adjacent chains. Aliphatic amido diols were synthesized by the aminolysis of gamma-butyrolactone, delta-valerolactone and epsilon-caprolactone with aliphatic diamines containing a number of methylene groups from two to six in isopropanol medium at room temperature. Effects of polarity of the solvent on solution polymerization and effect of catalyst on trans esterification were studied. These polymers were characterized by elemental analysis, FTIR, H-1 NMR, C-13 NMR, solubility studies, inherent viscosity, DSC, X-ray diffraction, polarized light microscopy, and TGA. All the melt/solution polycondensed PEAs showed multiple-phase transitions on heating with second transitions identified as nematic/smectic/spherullitic texture. The mesomorphic properties were studied as a function of their chemical structure by changing alternatively m or n. Odd-even effect on mesophase transition temperature, isotropization temperature, and crystallinity were studied. The effect of molecular weight and polydispersity on mesophase/isotropization temperature and thermal stability were investigated. It was observed that there exists a competition for crystallinity and liquid crystallinity in these PEAs.