This paper describes the influence of electrolytic water dilute NaCl on the surface of Fe-42wt% Ni alloy (it is abbreviated to alloy 42 hereafter). First, we clarified the etching characteristic of electrolytically-oxidized water and electrolytically-reduced water against alloy 42 by the immersing experiments. What becomes clear is that electrolyticallyoxidized water has twice as big etching ability as HCl solution and that there is no etching operation in electrolyticallyreduced water. Next, we clarified two things by the surface analysis of the test pieces. One is that both electrolytically-reduced water and electrolytically-oxidized water are able to improve the cleanliness of the surface of the alloy 42. The other is that the oxide film layer can become thick by immersion into the electrolytically-oxidized water. The study indicates that electrolytic water can be applied to washing process of alloy 42 surface.