The solid state processing ability of semicrystalline polyamides is particularly complex, owing to their degree of polymorphism. Among polyamides, the crystalline structures of PA6 and PA11 have been extensively studied. PA6 exhibits two crystal phases (alpha and gamma)characterized by a sheet-like H-bonded structure and one mesophase (beta) with pseudo-hexagonal symetry where the H-bonds are randomly distributed. Each crystalline form may be promoted, depending on elaboration conditions, and each exhibits distinct properties. Whereas the less ductile alpha phase is highly stable, whatever the thermomechanical history, the beta form progressively transforms into alpha phase, both thermally and under stretching. This thermomechanically induced sheet-like H-bonded phase is assumed to be the source of the poor abilitity of PA6 for biaxial stretching. In the case of the biobased PA11, up to five crystal phases have been identified at room T. Some of them also adopt a sheet-like H-bonded structure, such as the so-called alpha' phase. However, unlike the case of PA6, a Brill transition is well recognized for PA11: for instance, the room temperature alpha’ phase exhibits a reversible crystal-crystal transition upon heating. Although the nature of the Brill transition is still unclear, it seems that a rearrangement of hydrogen bonds into intersheet directions occurs at high temperature, resulting in a loss of the sheet-like structure. Several studies have dealt with the crystal transitions occuring in PA11 upon heating but only scarce information is available regarding the deformation induced crystal transitions in relation to the initial structure.The present study is thus focused on the uniaxial and biaxial drawing behavior of PA11 below and above the Brill transition. The mechanical response of PA11 and PA6 are compared in the light of their structural evolution. The latter is investigated by means of WAXS and FTIR spectroscopy. Moreover, in order to gain a better understanding of the key structural events related to the drawing of PA11, an in-situ study of the uniaxial stretching behavior has been performed on the BM02 synchrotron beamline at ESRF,Grenoble.