Characteristics of the adsorption isotherms of water vapor on active carbons from coal and coffee grounds and those ozonized ones from the surface fractal dimension analysis are discussed. The upswing of the adsorption isotherms in the low relative pressure of coffee grounds-based active carbon, of which isotherms were not scarcely affected on ozonization, was attributed to the adsorption of water molecules on the metallic oxides playing the role of oxygen-surface complexes, which formed the corrugated surfaces on the basal planes of micropore walls with the surface fractal dimension Ds > 2. On the other hand, coal-based active carbon with Ds < 2, which indicated the flat surfaces of micropore walls, showed little effect on the upswing even on ozonization, even though the adsorption amounts of water vapor were increased in the low relative pressure. Copyright 1998 Academic Press.