To provide a method of treating arsenic-containing solution such as industrial wastewater or environmental water and efficiently removing an arsenic concentration in the solution.

In the method of removing arsenic for magnetically separating adsorbent brought into contact with arsenic-containing solution, the adsorbent is a magnetic chelate material in which a chelate group bearing a metal ion is introduced via an organic polymer or a magnetic chelate material in which an amino polyol group as a chelate group is introduced via an organic polymer.