The amount of micropore and monolayer absorbed on the external surface of adsorbents were obtained from the αs-plots of argon adsorption isotherms at 77K on untreated or surface-treated silica gels and activated carbons. A three-parameter adsorption equation can be used to predict the isotherms reduced by their micropore amounts throughout nearly the entire relative pressure range. The amounts of monolayer thus obtained agreed with the amounts of external monolayer obtained from their αs-plots. The three-parameter adsorption equation can also be used to predict their bulk isotherms with a reduction of the amount of micropore. The amount of monolayer thus obtained agreed with the sum of the amounts of the micropore and monolayer on the external surface of the adsorbent. The micropore of activated carbon is found to be much finer than that of silica gels, and the cross sectional area of the adsorbed adsorbate molecule in the micropore of activated carbon is also found to be smaller than that of the usual adsorbate molecule, because of the strong interaction due to the wall of the micropore.