Basic structural data of two sequential poly(ester amide)s derived from glycolic acid, 1,6-hexanediamine, and adipic acid or dodecanodioic acid have been determined by means of X-ray and electron diffraction patterns from fibers and single crystals. Chain-folded lamellar crystals were obtained by isothermal crystallization from diol or glycerine solutions, and the crystalline habit was investigated by real space electron microscopy. Polyethylene decoration techniques were applied to evaluate the regularity of the folding surfaces. Spherulites prepared from evaporation of formic acid solutions were also studied. The two sequential poly(ester amide)s crystallized according to triclinic and monoclinic unit cells, in which the a crystallographic parameter was close to the typical distance between hydrogen-bonded chains. Projections viewed down the chain axis revealed differences in the packing mode since oblique and rectangular cells were found for the adipic acid and dodecanodioic acid derivatives, respectively. Both structures can be envisaged as a stacking of hydrogen-bonded sheets although clear differences concerning the shift between consecutive sheets and the number of layers comprising the unit cell were found. The large unit cells that have been deduced seem to be a consequence of the different packing preferences of the diester and diamide moieties. Both polymers have a molecular conformation that deviates from the all-trans conformation typical of aliphatic polyamides and polyesters with a large number of methylene groups. (C) 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 194-206, 2009