Two mesogenic homologous series involving ester-azo central linkages with a biphenyl moiety have been synthesized, such as 4 '-[(4-n-alkoxyphenyl)diazenyl]biphenyl-4-ol (series I) and 4 '-[(4-n-alkoxyphenyl) diazenyl]-4-butoxy phenyl biphenyl-4-carboxylate (series II). Azobiphenyl of series I having a free hydroxyl group with strong hydrogen bonding exhibits a high-temperature enantiotropic smectic phase. Whereas in series II, compounds containing C-1-C-8 carbon atoms exhibit only a monotropic smectic phase and compounds with C-10, C-12, C-14, and C-16 atoms show an enantiotropic smectic phase. These compounds were characterized by elemental analysis, FT-IR, H-1-NMR, and mass spectral studies. The phase transition and mesogenicity of these substances were studied by polarizing optical microscopic and differential scanning calorimetric techniques. Their thermal stabilities and other characteristics are discussed.