To inhibit the swelling of PVA membranes in aqueous alcohol solutions, which leads to lowered water permselectivity during separation, organic-inorganic hybrid membranes composed of poly(vinyl alcohol) (PVA) and tetraethoxysilane (TEOS) were prepared. When an aqueous solution of 85 wt % ethanol was permeated through the PVA/TEOS hybrid membranes during pervaporation, the separation factor for water permselectivity increased, but the permeation rate decreased, with increasing TEOS content. We concluded that the decreased permeation rate was caused by decreasing the degree of swelling of the membrane. Therefore, this decrease in the degree of swelling and. the increase in membrane density were due to the formation of hydrogen bonds between the silanol groups resulting from the hydrolysis of TEOS and the hydroxyl group of PVA. When the PVA and PVA/TEOS hybrid membranes were annealed, the separation factor of these membranes increased with increasing annealing temperature and time. The fact that annealing at higher temperatures promoted the dehydration-condensation reaction between PVA and TEOS in PVA/TEOS membranes was related to the enhanced permselectivity of the PVA/TEOS membranes.