<p>In this study, a series of poly(ethylene succinate)-<i>b</i>-poly(butylene carbonate) (PES-<i>b</i>-PBC) multiblock copolymers were prepared through the chain-extension reaction of hydroxyl-terminated PES (PES-OH) and hydroxyl-terminated PBC (PBC-OH) prepolymers with 1,6-hexmethylene diisocyanate (HDI) as a chain extender. The effects of the prepolymer molecular weight and content on the structure and application properties of the PES-<i>b</i>-PBC copolymers were systematically investigated using various techniques. It was found that the compatibility of PES and PBC blocks in PES-<i>b</i>-PBC copolymers can be greatly enhanced by lowering the length of the prepolymers, and the amorphous phase of the PES and PBC chain segments in the PES-<i>b</i>-PBC copolymer would transform from immiscibility and partial miscibility to miscibility when the number-average molecular weight (<i>M</i>_n) of the PES-OH and PBC-OH prepolymers is less than 2000 g/mol. Only the crystal structure of bare PES can be observed in the wide-angle X-ray diffraction (WAXD) spectrum of the PES-<i>b</i>-PBC copolymers, but their crystallinity degrees were found to decrease with increasing PBC fraction. The thermal behavior, crystallization performance, rheological properties, mechanical properties, and degradation properties of the PES-<i>b</i>-PBC multiblock copolymers can be easily modulated by altering the block length and composition of the prepolymers, offering potential applications in biodegradable materials.</p>