T he sorption, desorption and solubility of vapour and liquid water in polyvinyl alcohol (PVA) membranes treated by formaldehyde was studied. The sorption and solubility of water in PVA membranes with different degrees of maleic acid crosslinking was also investigated and compared with that of the forrnaidehyde-treated membranes. The structural differences that arise as a consequence of these two treatment methods and the corresponding differences in the diffusivity and solubility of water molecules are discussed. In addition, the key step involved in the dehydration of benzene using PVA membranes treated by formaldehyde was analysed. Three common models for pervaporation process are compared.