<p><P>PROBLEM TO BE SOLVED: To provide an organohalogen compound decomposing agent that uses as a raw material iron chip, iron scrap and the like which have not been allowed so far to be used for the purification of groundwater or the like contaminated with an organic compound because its low performance and has high purification performance, to provide a process for producing the decomposing agent, and to provide a purification process using the decomposing agent. <P>SOLUTION: The process for producing an organohalogen compound decomposing agent comprises an acid washing step of washing iron powder having an oxide film and a heating step of heating the washed iron powder in an oxidizing atmosphere. Preferred is an embodiment that the heating temperature in the heating step is 40-120°C. <P>COPYRIGHT: (C)2010,JPO&INPIT</p>
