To inexpensively provide foil and a method for producing the same without using a complex device, wherein the foil has a high surface enlargement ratio per unit volume by densely arranging pit formation positions of the foil to be subjected to surface enlargement treatment, especially the foil used for an electrode for an electrolytic capacitor.

The method for producing foil treated for surface enlargement and the foil produced by the method are provided, wherein a mask having predetermined openings is produced, which preliminarily produced mask is placed in close contact with at least one surface of the foil, and the surface enlargement treatment is performed on the foil by etching the foil with the openings of the mask and creating pits on the foil.