Abstract: Scorodite-type iron-arsenic compound particles in which the particle surface layer part comprise an iron-rich layer having an Fe/As molar ratio of at least 1.24. The particles can be obtained in a reaction process of feeding an oxygen-containing gas to an aqueous solution containing an arsenic(V) ion and an iron(II) ion to precipitate a scorodite-type iron-arsenic compound crystal at a pH of at most 2, in which an oxidizing agent is further added to the liquid before the end of the reaction (treatment A). The particles may also be obtained by a method comprising keeping a scorodite-type iron-arsenic compound particle of good crystallinity in contact with an iron ion-containing aqueous solution having a controlled pH of from 2 to 9 at 0 to 90° C. (treatment B). The scorodite-type iron-arsenic particles have good filterability and excellent arsenic release-preventing effect.