The cold drawing of a poly(ether ester) block copolymer was studied by in-situ simultaneous small- and wide-angle X-ray scattering techniques in combination with a tensile stretching apparatus. The results obtained revealed three distinct regions in the stress-strain relationship. At low strains (0 < epsilon < 18%), the applied stress caused extension of the amorphous regions, formed by PTMO and some noncrystallizable segments of PBT, and subsequently reorientation of PBT crystalline lamellae. At slightly higher strains the lamellae become perpendicularly aligned to the drawing direction. At intermediate strains (18% < epsilon < 80%), the elongation gradually leads to breakage of the lamellae into smaller pieces, which eventually formed microfibrils containing linear assembly of layered lamellae. At large strains (E > 80%, a further extension of the PTMO amorphous chains resulted in the fracture of the sample. The pathway of the structural changes by deformation in the present study was slightly different than those observed in the predrawn samples.