Structual change of untreated and salt-treated drawn polyacrylonitrile(PAN) fiber has been studied with IR spectroscopy, wide angle X-ray diffraction, dynamic mechanical measurements, thermo-mechanical analysis, and tensile propert irs measurements. The results are interpreted in terms of the degree of bound nitrile groups based on two-phase structure, ordered and disordered region. The salt treatment resulted that the crystalline size and the degree of lateral ordered crystallinity were increased. The bound nitrile groups in ordered and disordered region of salttreated PAN fiber were lower than these of untreated fiber