PURPOSE: To produce an adsorbent having heat resistance and radiation resistance and excellent in adsorbing characteristic to Sr ion by using an inorg. ion exchange body expressed by a specified composition formula.

CONSTITUTION: The inorg. ion exchange body expressed by the formula SnO2.aSb2O5.nH2O is used for this absorbent. In this case, (a) is a number satisfying 2≤a≤10 and (n) is zero or a positive integer. Since this adsorbent is markedly large in Kd(Sr) in an acidic aq. soln., in other wards, extremely large in Sr ion adsorbing ability from the acidic aq. soln. dilute in Sr ion concn. Moreover, this adsorbent has heat resistance and radiation resistance. Consequently, this adsorbent is useful for treatment of a radiation nuclear species- containing matter, especially for water treatment such as a treatment of a waste liq. containing Sr ion discharged from a nuclear plant such as a nuclear power plant and a nuclear fuel reprocessing plant.