A new sequential poly(ester amide) derived from 1,12-dodecanediol, sebacic acid, and glycine was synthesized and characterized, its crystalline structure was studied with transmission electron microscopy and X-ray diffraction. The results were compared with results for a related polymer, derived from glycine, 1,6-hexanediol, and succinic acid, that produced a lower methylene/carbonyl ratio. The crystalline structures of both polymers corresponded to a periodic arrangement of two layers of hydrogen-bonded molecular chains, whose polymethylene sequences mimicked the packing of polyethylene and the majority of polyesters.