There is provided a method for recovering a powder of a compound of iron and arsenic, which has a very low concentration of arsenic eluted from the powder, by treating an arsenic containing solution, e.g., a high purity and high concentration arsenic containing solution obtained by treating an arsenic containing substance which contains various elements other than arsenic, such as an intermediate product in a non-ferrous metal smelting or refining process. Ferrous ions are added to an arsenic containing solution, which contains 10 g/L or more of arsenic, so as to cause the ratio (Fe/As) of iron to arsenic in the solution to be not less than 1, and an oxidizing agent is added to the solution to allow a reaction at a temperature of not lower than 70.degree. C. while stirring the solution. Then, a solid-liquid separation is carried out, and a solid part separated by the solid-liquid separation is dried.