The paper is an attempt to explain the mechanism of water adsorption on carbonaceous adsorbents with high-enemy centers (surface or cation-exchange groups). The equations formulated previously by Dubinin et al. and Barton et al. are analyzed. Thus, four types of empirical factors defining the decrease in adsorption site concentration are taken into account. The isotherms of water adsorption measured on two microporous activated carbons containing various densities of hydrophilic sites are described by the above-mentioned theoretical isotherm equations. It is shown that none of these models provides an adequate description Of the experimental data. especially at low relative pressures. This leads to the conclusion that with regard to the Dubinin and Serpinsky theory. the chemisorption of water at very high-energy adsorption sites needs to be taken into account. In view of the above, a new theoretical relationship is proposed which includes a correct description of the decreasing number of active sites. As a consequence, a good correlation between the new theoretical model and experimental data is observed over the whole range of relative pressures. (C) 2004 Elsevier Inc. All rights reserved.