There is provided an iron arsenate powder which is produced from an arsenic containing solution and wherein the concentration of arsenic eluted or released from the powder is very low. The iron arsenate powder is a powder of dihydrate of iron arsenate, which has a mean particle diameter of not smaller than 8 micrometers, preferably not smaller than 10 micrometers, and a BET specific surface area of not greater than 2 m.sup.2/g, preferably not greater than 0.5 m.sup.2/g, and wherein the percentage of particles having particle diameters of not greater than 5 micrometers of the powder is not greater than 10%, preferably not greater than 5%. The amount of each of calcium and magnesium contained as impurities in the iron arsenate powder is preferably not greater than 2% by weight.