The influence of water absorption on polyethylene oxide and its complexes with NH4ClO4, NaClO4 and Mg(ClO4)(2) (for O/M = 10 and 3) has been studied. A quantitative estimation of water absorption kinetics has been carried out. The changes in microstructure and thermal behaviour due to water absorption have been studied using X-ray diffraction and thermogravimetric/differential thermal analyses. The electrical conductivity of different films has been measured as a function of relative humidity and explained in terms of the generation of free mobile ions due to water absorption.