Although the microdomains of polymeric systems including the thermoplastic elastomers in the as-spun electrospun fiber were reported, the orientation of microdomains has not yet been well clarified. The present work shows an existence of microdomain orientation through a case study of a well-aligned electrospun fibers of polystyrene-block-poly(ethylene-co-1-butene)-block-polystyrene triblock copolymer (SEBS) obtained from an electrospinning unit equipped with a rotational disk fiber-collector. Two-dimensional small-angle X-ray scattering (2D-SAXS) patterns of the as-spun electrospining SEBS fibers show elliptical and four-point patterns suggesting an orientation of distorted and fragmented lamellar microdomains. The electrospun fibers obtained from a low rotational disk collector speed (31.5 m/min) exhibits a significant microdomain distortion whereas the fibers obtained from high take-up velocities (310 m/min, 620 m/min, and 1240 m/min) show higher fragmented-microdomain stretching. By annealing the electrospun fibers, the fibers develop an isotropic SAXS pattern with traces of the remained anisotropic orientation. Based on the above mentioned evidences in SEBS, the present work, for the first time, clarifies that the as-spun thermoplastic elastomers fibers show not just a simple microdomain as used to be observed by transmission electron microscope (TEM) but rather with orientation which can be confirmed by SAXS. (C) 2010 Elsevier Ltd. All rights reserved.