Biodegradable poly(ethylene succinate-co-diethylene succinate) (P(ES-co-DEGS)) copolyesters with different diethylene glycol succinate (DEGS) compositions and the homopolymer poly(ethylene succinate) (PES) were successfully synthesized by a two-stage melt polycondensation method. The crystal structures, basic thermal properties, crystallization kinetics, and spherulitic morphologies of P(ES-co-DEGS) and PES were extensively investigated. Relative to PES, the glass transition temperature values of the copolyesters are slightly reduced, while their melting temperature and equilibrium melting temperature values obviously become smaller. The crystal structures of the copolyesters are the same as PES, while their degree of crystallinity values are slightly reduced. Relative to PES, the crystallization rates of the copolyesters become smaller, while the crystallization mechanisms remain almost unchanged. The morphology study revealed that the enhanced spherulite size and lowered nucleation density were observed with increasing crystallization temperature for all of the samples. (C) 2015 Elsevier B.V. All rights reserved.