Aiming at the improvement of mechanical and dielectric properties of poly(vinyl alcohol) (PVA), we prepared composites of PVA and magnesium nitrate hexahydrate. It was found that the composites were very soft and rubber-like, and the glass transition temperature decreased with increasing the salt concentration. Wide-angle X-ray diffraction and small-angle X-ray scattering revealed that the crystallites of PVA were destroyed by the additive and it was the cause of the softening. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112: 1647-1652, 2009