Effects of cyclodextrin (CD) on the pervaporation characteristics for water/ethanol through the PVA/CD membranes (PVA membranes containing beta-CD oligomer) have been investigated in terms of sorption equilibria and diffusion coefficients based on the sorption-diffusion theory. The increase in water selectivity through the pervaporation by CD was due mainly to the changes in the diffusion coefficients by CD, which depended on the feed composition and the cross-linking time. The water selectivity through the sorption equilibria was not increased by the addition of CD, and the ethanol-sorption amount was increased by CD. These effects of CD were interpreted by the inclusion strength in the CD cavity and the cross-linking density of the PVA phase.