Poly(vinyl alcohol) (PVA)/iodine polarizing film was manufactured as follows: PVA iodinated in solution before casting (IBC film) and iodinated again after casting (IBC + IAC film) and then the IBC + IAC film was drawn in boric acid aqueous solution (IBC + IAC polarizing film), to improve the durability of the polarizing film under a humid and warm atmosphere. These effects were examined by investigating the structural and optical properties of the IBC, IBC + IAC, and IBC + IAC polarizing films. In the IBC state, the PVA chain segments that combined boric acid and iodine were regarded as defects of the crystal, the formation of I-3(-) decreased with respect to weight gain of boric acid. In the IBC + IAC state, the strength of the peak corresponding to I-3(-) decreased and the I-5(-) peak increased. The iodine ions penetrated into crystal of the IBC state during the IAC process and formed a new PVA/iodine complex crystal at the 2 theta = 20 degrees in the X-ray diffraction curves. In the IBC + IAC polarizing film state, another type of polarizing film (IBC + IAC polarizing film-H) containing I-3(-) ions mainly was manufactured as well as the IBC + IAC polarizing film to compare the effects of the I-3(-) and I-5(-) ions on the durability of the polarizing films. The durability of the I-3(-) ions that were complexed with the PVA chain was higher than the I-5(-) ions, which could possibly be separated to I-3(-) and I-2. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 120: 397-405, 2011