It has been highly desirable to develop high-performance thermoplastic polyesters that are strong, tough, and highly stretchable, in addition to high glass transition and excellent optical properties. The performance portfolio is essential for the practical applications of polyesters in high-end areas of aerospace, energy, medical sterilization, and optics. However, current material design strategies have failed to endow polyesters with such integrated performances. Herein, we report the facile synthesis of modified copolyesters with multiple hydrogen bonds (H-bonds) on the main chains via condensed polymerization. The resultant copolyester records a break strain as high as 438% and a large toughness of 106.7 MJ/m(3), representing the most stretchable and toughest thermoplastic polyesters so far, while exhibiting a high tensile strength of 59.6 MPa because of intermolecular multiple H-bonding. In addition to achieving an enhanced glass transition temperature (similar to 85.9 degrees C), the copolyester films exhibit improved postcrystallization optical transparence and good flexibility due to the grain refinement effect. This work provides an innovative design concept to prepare a new class of advanced polyesters with outstanding mechanical, thermal, and optical properties, thus holding great promise for many potential industrial applications.