4-Hydroxybenzaldehyde or 3-methoxy-4-hydroxybenzaldehyde was condensed with cyanoacetic acid to afford 1-hydroxy-4-(2-cyano-2-carboxyvinyl)benzene (1) and 1-hydroxy-2-methoxy-4-(2-cyano-2-carboxyvinyl)benzene (2) respectively. They were converted to the corresponding acid chlorides by reacting with thionyl chloride and polycondensed in the presence of pyridine to afford unsaturated cyano-substituted homopolyesters. In addition, various copolyesters were prepared from the acid chlorides of 1 and 4-hydroxybenzoic acid. The polyesters were characterized by Fourier-transform infra-red spectroscopy and differential thermal analysis as well as by inherent viscosity, X-ray and water absorption measurements. They softened between 100 and 200 degrees C, were amorphous and showed higher hydrophilicity and solubility in certain organic solvents than did the reference polyester prepared from 4-hydroxybenzoic acid. The crosslinked polymers obtained by curing at 300 degrees C for 48 h were remarkably more thermally stable than the cured reference polyester. They were stable up to 291-355 degrees C in N-2 or air and afforded anaerobic char yield of 49-68% at 800 degrees C. The thermal stabilities of cured polyesters were correlated with their composition.