PURPOSE: To improve pertaining to the electrostatic capacitance of an electrolytic capacitor by a method wherein an aluminum foil for an electrolytic capacitor having on average concentration of lead contained in the surface layer part or 10W100 ppm is used.

CONSTITUTION: When the average lead concentration of the layer from the surface to the depth of 0.1 μm is 10W100 ppm, desirably when the average concentration of lead contained in the layer from the surface to the depth of 0.05 μm is 14W150 ppm, the number of tunnel pits is increased, and the decrease in surface area due to incorporation is small. The number of tunnel pits becomes small when the lead present on the surface layer is 10 ppm or less, and when the lead concentration exceeds 100 ppm, the surface area of the etched foil is reduced on the contrary by the generation of consolidation of the tunnel pits. There are a plating, a sputtering, a flame spraying, a vapor deposition, and a cludding methods and the like as the method in which lead is added to the surface layer of the electrolytic capacitor.