The sizes of cylindrical uniform pores on solid surfaces were estimated by experiments on adsorption of n-butylbenzene vapor and krypton gas with anodized aluminum and silicon plates as samples. All adsorption isotherms had significant hysteresis loops due to capillary condensation, which showed the apparent pore volume of the samples. The adsorption isotherm of krypton used in the BET method gave total surface area, including the inside surface area of pores, and the isotherm of n-butylbenzene vapor gave the outer surface area excluding the inside pore surface area using the "gradient method." Thus, uniform pore size was calculated from the apparent pore volume and the total inside area of the pores. Pore sizes agreed well with those expected under anodizing conditions for the aluminum samples. The adsorptive pressure at which capillary condensation began or was released from the pore was consistent with the capillary-condensation pressure calculated by the Kelvin equation. A significant finding was that capillary condensation ended, for cylindrical pores closed at one end on anodized aluminum and silicon samples, at a relative pressure corresponding to the square root of the initial relative pressure of capillary condensation. It was found that uniform pore size could be estimated at from 150 to 1.7 nm, using adsorption/desorption hysteresis of the adsorption isotherms of n-butylbenzene vapor.