In order to improve the viscoelasticity and foamability, poly (butylene succinate) (PBS) was modified through reactive melt mixing with chain extender (CE) having multi epoxy-groups. Subsequently, the prepared chain extended PBS (CEPBS) was foamed in a high pressure stainless steel autoclave using CO2 as physical blowing agent. The molecular weight, thermal properties, rheological properties, and foam properties of various PBS samples were characterized using gel permeation chromatography, differential scanning calorimetry, rotational rheometer, and scanning electron microscope, respectively. With the introduction of CE, the molecular weight, the crystallization temperature, the complex viscosity and storage modulus of PBS were increased and the crystallization degree of PBS was decreased. At the CE content of 0.75 phr, the cross-linking structure was formed and the expansion volume ratio increased to nearly 15 times, which meant the chain extension played an important role in the foaming process of PBS. POLYM. ENG. SCI., 55:988-994, 2015. (c) 2014 Society of Plastics Engineers