Poly(butylenes succinate) (PBS) is a kind of biodegradable polymer with excellent mechanical and thermal properties. This work has investigated the foaming property of PBS and its blends with an amorphous semi-aromatic nylon poly(hexamethylene (iso-co-tere)phthalamide) (PA6IcoT) using supercritical CO2 as the blowing agent. The results showed that the average cell diameter and cell density of PBS foam obtained at 28MPa and 120oC are 40m and 5.9107/cm3, respectively. The presence of PA6IcoT in the blends prevent the cell coalescence and induce more heterogeneous nucleation, resulting smaller cell size and higher cell density in the foams. Using the reactive blends of PBS and PA6IcoT with a weight ratio 90:10, the foams with cell size as small as 8m and cell density as high as 2.0109/cm3 can be obtained. Furthermore, the foams made from blends can also have a bimodal cell size distribution.