Solid polymer proton conductors comprising of poly(vinyl alcohol), ammonium acetate and water have been prepared by solution cast method for different NH4+/OH- ratios. The XRD spectra for the electrolyte indicate that the amorphous nature of PVA increases with the concentration of ammonium acetate. The DSC curves show the low glass transition temperature for the ratio (NH4+/OH-) = 0.25 which relates to higher conductivity of the sample. The ionic conductivity at room temperature depends strongly on NH4+/OH- ratios. The variation of electrical conductivity with temperature showed two regions of activation above and below glass transition temperature. The optical absorption studies show the similar trend for pure PVA and salt-doped PVA with different absorption intensity. The direct and indirect band gap energy is observed to be constant for pure PVA and salt-doped PVA samples and found to be 5.4 eV and 4.8 eV, respectively. The dc polarization measurement shows that the conductivity is mainly due to ions. (c) 2005 Elsevier B.V. All rights reserved.