Simultaneous measurements of microscopic infrared (MiGIR) dichroism, mesoscale deformation, and macroscopic stress during uniaxial stretching are made to four microphase-separated poly(ether-block-amide) (PEBA) films quenched form melt. Before the onset of microstructural alterations, poly(tetramethylene oxide) (PTMO) blocks in soft domains undergo affine deformation, and the true stress-strain relationship on the mesoscale of 500 mum can be described using an interpenetrating network model combining the Matsuoka viscoelastic constitutive equation and the affine deformation equation for mechanically hard and soft networks, respectively. Beyond a threshold strain at which PTMO blocks in the soft network are fully extended, plastic deformation occurs in the hard domain composed of polyamide-12 (PA), which is accompanied by depression of the true stress toward values lower than the prediction of the interpenetrating network model and also by deviation of the molecular orientation of PTMO blocks in the soft domain from the affine deformation mode. The deformation in the hard domain is characterized by a three-stage molecular orientation of hard PA blocks being present in either a fibrillar or a lamellar form. Alignment of PTMO blocks along the draw axis is predominantly observed for the sample with the lowest PA fraction, followed by rotation of the lamellae and then by the plastic deformation leading to fibrillation at high strains.