In this work, a biodegradable polymer composite was prepared by mixing poly(ethylene succinate-co-5.1 mol 96 ethylene adipate) (PESA) and octavinyl-polyhedral oligomeric silsesquioxanes (ovi-POSS) at a very low ovi-POSS loading. It is found that a fine dispersion of ovi-POSS has been achieved in the PESA matrix. The effects of ovi-POSS on the nonisothermal melt and cold crystallization behaviors, overall isothermal melt crystallization kinetics, spherulitic morphology, and crystal structure of PESA in the composite were studied in detail with various techniques. Relative to neat PESA, both the nonisothermal melt and cold crystallization behaviors and isothermal melt crystallization kinetics of PESA have been enhanced significantly in the composite. Ovi-POSS is an efficient nucleating agent for the crystallization of PESA, because the nucleation density of PESA spherulites is apparently higher in the composite than in neat PESA; however, the crystallization mechanism and crystal structure of PESA remain unchanged in the composite.