Abstract: Poly(butylene succinate) (PBS) was modified by chain extension through reactive melt mixing in a torque rheometer using ADR-4370S as a chain extender. Molecular structure and thermal and rheological properties of the modified PBS samples were investigated by torque rheometer, gel content test, differential scanning calorimetry, and rotational rheometer. PBS foams were prepared by using supercritical carbon dioxide as physical blowing agent in an autoclave. Foaming properties of PBS foams were characterized by scanning electron microscopy and densimeter. The results indicated that there was structural change in PBS macromolecules from linear to branched or cross-linking structure due to the chain extension. The branched PBS foam could obtain an optimum cell morphology with the addition of 1.5 phr chain extender at foaming temperature of 105 ℃.