This paper describes the etching effects of Na₂SO₄ electrolyzed oxidizing water on the surface of pure iron. First, we threw light on the etching characteristic of electrolyzed oxidizing water on the surface of pure iron by comparative immersion experiments with H₂SO₄ solution. The results show that etching effects of electrolyzed oxidizing water are huge. In addition, the higher the ORP/pH value of the electrolyzed oxidizing water becomes, the quicker the etching effects works. Next, we threw light on the influence of electrolyzed oxidizing water on the surface shape of pure iron, by the observation using the SEM image. The results indicated that electrolyzed oxidizing water did not have a big influence on the surface shape of pure iron. Lastly, by analyzing the surface, we made it clear that electrolyzed oxidizing water had no bad influence on the chemical composition of the pure iron surface. The study indicates that Na₂SO₄ electrolyzed oxidizing water can be applied to the surface treatment and washing of pure iron. Na₂SO₄ electrolyzed oxidizing water does not have chloride ion, unlike NaCl electrolyzed oxidizing water. Therefore, Na₂SO₄ electrolyzed oxidizing water is wide in the application scope, compared with NaCl electrolyzed oxidizing water.