Ethylene nanoextrusion polymerization has been demonstrated to be a novel nanofabrication concept for the preparation of polyethylene (PE) fibers directly from ethylene monomers without any post-processing procedures. For PE fibers, chain orientation is a critical parameter that affects performance and application of the fibrous materials. In this communication we report an investigation on chain orientation in PE fibrous samples prepared through nanoextrusion polymerization using a two-dimensional wide angle X-ray diffraction (2D WAXRD) technique. Two types of fibrous samples,including individual microfibers and microfiber aggregates, were sampled randomly and studied. For individual PE microfibers, anisotropic diffraction patterns were observed, suggesting chain orientation along the microfiber axial direction. Some microfibers showed the most desired diffraction pattern often found in high modulus high-strength PE fibers. These samples possessed a very high degree of chain orientation along the fiber axis. Owing to a random aggregation of anisotropic microfibers, microfiber aggregates exhibited isotropic diffraction patterns. This work provided further experimental evidence for the proposed nanoextrusion polymerization concept.