Structural characterization of poly(dodecamethylen-di-O-methyl-L-tartar-amide) was carried out with optical microscopy, thermal analysis, X-ray diffraction, and electron microscopy. Two different crystalline forms were found in accordance with the thermograms, powder and fiber X-ray diffraction diagrams. The electron microscopy allows corroboration of the morphological and crystallographic differences. Molecular modeling was used to conclude the structural analogies and differences between the two crystalline forms that were related to the chain packing and orientation in the crystal cell, respectively.