The adsorption equilibria of water vapor on an alumina/zeolite 13X composite and silica gel were measured at 293.15, 303.15, and 313.15 K and at relative pressures (P/P-s) of up to 0.95. The experimental isotherms were compared with those of zeolite 13X and alumina. The data were correlated by the Dubinin-Astakhov (DA) model and the Aranovich-Donohue (AD) model using Sips and Toth isotherms. The heats of adsorption were in the range of 50-59 kJ center dot mol(-1) for silica gel but decreased from 75 to 45 kJ center dot mol(-1) for the alumina/zeolite 13X composite with increased loading. The composite showed much higher adsorption affinities and adsorption amounts than did silica gel in the low-pressure range, owing to the characteristics of zeolite 13X. However, at increased pressures, the isotherm shape for the composite was similar to that for alumina.