Nonlinear optical (NLO) rigid main-chain polyesters containing azobenzene mesogens with high thermal and temporal stabilities were synthesized from derivatives of hydroxyphenylazobenzoic acid. The NLO properties of the homopolymer, poly [4-(4,-hydroxy-3-methyl phenyl)azo]benzoic acid, and copolymers of 4-[(4-hydroxy-3-methylphenyl)azo]benzoic acid, 4-[(4-hydroxy-2-methylphenyl)azo]benzoic acid, and 4-[(4-hydroxy-2-pentadecyl phenyl)azo]benzoic acid (PSCpHBA) with p-HBA were measured by the Maker fringe technique. The thermal and liquid-crystalline (LC) phase behaviors of the polymers were examined by differential scanning calorimetry, a thermal-stimulated polarization current, and polarized light microscopy. The polymers except PSCpHBA exhibited nematic-threaded and Schlieren textures. The LC orientations give rise to an enhanced NLO response. The polymers had high thermal and temporal stabilities for second-harmonic generation activity because of their rigid aromatic backbone. This study suggests that the rigid aromatic main chain exhibiting an LC phase is a promising simple method to synthesize highly stable NLO polymers. (C) 2003 Wiley Periodicals,