A homologous series of mesogenic azo-esters having a terminal nitro substituent and methyl and chloro lateral substituents has been synthesized; the mesogenic behaviour of the series has been characterized. All the compounds are red, stable, and should have large positive dielectric anisotropies as the dipole-moment of the terminal nitro group is acting along the long axes of the molecules. The first member is non-mesogenic; the ethoxy to tetradecyloxy derivatives exhibit only nematic mesophases; the hexadecyloxy derivative exhibits smectic and nematic mesophases. The lateral substituents lower the crystal-mesophase and mesophase-isotropic transition temperatures.