Novel biodegradable copolymers derived from succinate, butan-1,4-diol, and butan-1,4-diamine were synthesized by two-step polycondensation reactions. The obtained copolymers had a periodical-sequence structure consisting of ester and amide units, and the melting temperatures of the periodic copolymers increased with an increase in amide content. The crystalline structure of the periodic copolymers differs from that of butylene succinate homopolymer (PBS), and these results suggest that the periodically introduced amide units are included in the crystalline phase forming a novel crystalline structure.