Thermal stresses were determined by a wafer bending technique for a newly developed family of all-aromatic and aromatic/aliphatic copolyester thermosetting films prepared by spin coating. The intrinsic stresses of the films were also estimated for T > T-g (glass transition temperature). The effects of chemical structure and film processing conditions on thermal stresses are discussed. Thermal stresses varied with temperature and processing conditions, and the variations were dependent upon the chemical structures and T-g of the copolyester films. The T-g＇s of different copolyesters were also estimated from thermal stress-temperature curves.