This paper describes the elucidation about the surface modification processing of permalloy 45 using Na₂SO₄-electrolyzed oxidizing water (It abbreviates as Na₂SO₄ EO water). Firstly, as for the influence of Na₂SO₄ EO water on the surface micro shape of permalloy 45 which was processed in the polish to the mirror surface, it was made clear using the results of FE-SEM observation and AFM measurement of the test pieces surface before and after immersion processing. The results is as follows. In the case of non-heating processing, if using Na₂SO₄ EO water compared with the H₂SO₄ solution and NaCl EO water, the test pieces surface is more uniformly done by the etching. In the case of heating processing, Na₂SO₄ EO water, H₂SO₄ solution and NaCl EO water are same and don't have big influence on the test pieces surface. Next, it reviewed about the removal of surface oxidation layer in the test pieces surface after heating processing. The results showed the surface oxidation layer can be more efficiently removed if using Na₂SO₄ EO water compared with H₂SO₄ solution; however, there is possibility that surface oxidation layer which is thicker than a natural-oxidation layer is formed. By this study, it got the possibility that Na₂SO₄ EO water can be applied to the surface modification processing of permalloy 45.