In this work we report the preparation of a series of alkaline solid electrolyte membranes, based on poly(vinyl alcohol) (PVOH), potassium hydroxide (KOH) and water (PVOH-KOH-H2O). They were characterized by electrical conductivity measurements using impedance spectroscopy (EIS), by thermal measurements, using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The most conducting membranes were composed of 45% PVOH, 15% of KOH and 40% wt. of water whose conductivity reaches the value of 2.3 x 10(-3) S cm(-1) at room temperature. Temperature dependence of conductivity was found to follow an Arrhenius type behavior rather than the free volume type behavior associated with ion transport mechanism on polymer motion. The conducting phases are established between the observed glass transition of the blends at about 190 K up to where the water content in the sample is completely dehydrated, that is to say, 450 K. The effect of the humidity on the electrolytic characteristics of a cell M \Polymer\ M (where M is stainless steel, silver) is quite remarkable. Changes in the conductivity of the polymer at room temperature between 1 x 10(-5) and 2.3 x 10(-3) S cm(-1) when the relative humidity changes between the 25 and 85%, respectively, have been observed. The results are explained in terms of the plastification effects of water on the polymer and the presence of a (KOH/H2O) separated phase in the polymer. This new alkaline solid electrolyte is interesting from the point of view of its potential application as humidity sensor or electrolytic separator in alkaline batteries. (C) 2003 Elsevier Science Ltd. All rights reserved.