We studied the effect of gap size on molecular orientation and crystalline structure of theuniaxially well-aligned nylon 6 nanofibers produced in the gap of the negatively charged metal plates. As evidenced by polarized FT-IR spectroscopy, relative intensity in several absorbance bands, including the N-H stretching, amide I, II, and III vibrations were found to be different in the parallel and perpendicular polarized FT-IR spectra. Moreover, X-ray analysis indicated that the metastable γ-form was predominant in the as-spun nylon 6 nanofiber, and was transformed into the thermodynamically stable α-form by increasing the cap size. These results suggested that the polymer chains were oriented perpendicular to the fiber direction. Molecular orientation to the fiber axis was enhanced as increasing the gap size.