The process of adsorption of dissociating organic substances from dilute aqueous solutions on various activated carbons is studied. The investigated adsorbents have different pore structure and chemical properties of the surface. The characteristics of activated carbons are determined from nitrogen and benzene isotherms and potentiometric titration data. The properties of pore structure-BET specific surface area, the total pore volume, the external surface area, the micropore volume, and the density of surface charge-are evaluated. The isotherms of benzoic acid adsorption from the aqueous phase are measured for a nide range of solution pH and constant ionic strength by using the static method. The liquid adsorption data are analyzed in terms of the theory of adsorption on heterogeneous solids.