Poly (1,4-dioxan-2-one)(PPDO)/starch blend is a novel biodegradable polymer system, and it has potential applications in preparing various low-cost environmentally friendly materials. In order to understand the relationship between their structure and properties, the thermal transition, crystallization and spherulitic morphology of PPDO/starch blends have been studied by means of differential scanning calorimetry (DSC) and polarized optical microscopy. It was found that when 5wt% starch was added to PPDO, a clear nucleating effect was observed. When the blends were crystallized from the melt, they formed banded spherulites that exhibited a well-defined Maltese cross depending on the crystallization temperature. Avrami exponents and crystallization rate constants of the blends with 5wt% starch were higher than those of PPDO and those of the blends with 10wt% starch. Both the dynamic DSC results and isothermal crystallization data indicated that the starch, with a content of 5wt% in the blends, acted as the nucleating agent for PPDO.