This paper discusses the basic characteristics of electrolyzed oxidizing water of dilute Na₂SO₄ and the etching effects on the surface of metals. First, the structure and the characteristics of the electrolyzed oxidizing water producing system as well as how electrolyzed oxidizing water of dilute Na₂SO₄ is produced by it are described. The electrolyzed oxidizing water producing system used in this study is the one with three tanks. Next, the relation between the characteristic value of electrolyzed oxidizing water and the value of electrolyzed electrolytic-current is investigated experimentally. How the characteristic value of electrolyzed oxidizing water changes as time passes is also investigated in the same way. Lastly, using the result of the experiment on the etching of pure iron material, the oxygen-free copper material and the alloy of copper and nickel, this paper elucidates the characteristics of electrolyzed oxidized water of Na₂SO₄.