AbstractAs a new biodegradable poly(ester carbonate), poly(butylene succinate‐co‐butylene carbonate) (PEC) is a random copolymer, which is composed of butylene succinate unit and butylene carbonate unit. The crystal structure, melting behavior, and morphology of PEC have been investigated by means of wide angle X‐ray diffraction (WAXD), differential scanning calorimetry (DSC), temperature modulated DSC (TMDSC), and optical microscopy (OM) in this manuscript. The crystal structure of PEC was found to be the same as that of poly(butylene succinate) (PBSU) through WAXD study, indicating that the butylene carbonate unit did not crystallize in the copolymer. Double melting behavior or one major melting endotherm with a shoulder was found on crystallizing PEC at various temperatures based on DSC study, which was explained by the melt‐recrystallization mechanism. The TMDSC experiment gave a direct proof for the melt‐recrystallization mechanism. The spherulitic growth of PEC was studied with OM at various crystallization temperatures. The spherulitic growth rates of PEC were analyzed by the Lauritzen‐Hoffman equation. The thermal parameters of PEC were compared with those of PBSU. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1556–1561, 2006