To produce a functionally gradient adsorbent with two inside-high and outside-low adsorptivity species formed in one solid grain by applying necessary treatment to the crushed grain and solid grain produced from the raw material.

A granular solid produced from the crushed grain and powder of crystobalite, tridimite and their mixture is phosphated and heat-treated (kept at 870°C for one hour and furnace-cooled, for example) to form two species having a different adsorptivity in one solid grain. Each formed layer has a high-adsorptivity core and low-adsorptivity shell, and the adsorbed component is not accumulated but diffused inward. The discharge of the internally adsorbed component to the periphery is minimized, an efficient action is revealed, and the adsorbent is semipermanently utilized with a simple treatment.