A decomposer for an organohalogen compound, containing iron particles comprising iron and iron oxide, wherein the iron particles have a metallic iron content of 15% or more by mass, wherein the metallic iron content is a content of metallic iron in the outermost surface layer of the iron particles to which the ion beam etching has been applied twice under the following etching conditions: degree of vacuum in a chamber: 2.0×10−2 Pa accelerating voltage of an ion gun: 10 kV emission current: 10 mA etching time: 14 seconds. The decomposer need not contain copper and has the ability to satisfactorily decompose an organohalogen compound. A method for producing the decomposer is also provided.