A theoretical analysis of γ-Al2O3 (110) surface hydroxylation based on ab initio Hartree–Fock embedded cluster calculations was carried out. Both tetrahedral and octahedral Al sites were considered. These sites were modeled by a series of clusters of increasing size: Al8O3, Al12O5, and Al16O8, embedded in an array of point charges. The adsorption of water was found to be dissociative or nondissociative depending on the cluster size, although the mechanism clearly converges toward dissociation for the more reliable models in agreement with the experiment. This dependence can be explained in light of the basicity modification of surface oxide ions induced by the environment as well as by surface relaxation. Comparison of chemisorption energies suggests that the preferred site for hydroxylation is a low coordination tetrahedral aluminum. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 70: 359–365, 1998