A method of selectively and efficiently adsorbing an anion such as a phosphate ion which adversely affect the environment when discharged without any treatment, or an anion which can be used beneficially when recovered, from waste water or a solution including such ion using an adsorbent. A method of adsorbing an anion of interest from an aqueous solution (A) containing the anion of interest and the other anion using an anion adsorbent, including performing at least (1) a step of contacting the aqueous solution (A) having a pH of 5.8 or less with the anion adsorbent to allow the anions to be adsorbed to the anion adsorbent, and then (2) a step of contacting water or an aqueous solution (B) having a pH of 5.2 to 11 with the anion adsorbent to desorb at least a part of the other anion adsorbed to the anion adsorbent from the anion adsorbent.