The nanostructure deformation mechanism of a predrawn and annealed blend of poly-(ethylene terephthalate) (PET) and polyethylene (PE)(PET/PE: 50/50 by wt %) was studied. For the first time six-point small-angle X-ray scattering (SAXS) patterns were observed as a function of elongation in the investigation of a drawn polymer blend fiber sample. It was found that the meridional two-point pattern arises from PET and the inclined four-point one from PE. Long spacings and the angle between inclined reflections and fiber axis were determined as a function of draw ratio. At lower external strain (elongation up to 13%) the macrodeformation is related to conformational changes located only in amorphous material outside the lamellar stacks, whereas at higher elongation destruction of layer crystallites is observed, possibly due to pull-out of chains.