Abstract: A welding method of an aluminum foil, which permits the direct resistance welding of an aluminum foil, with a chemical conversion coated layer of Al.sub.2 O.sub.3 formed thereon, to a lead wire, includes placing an aluminum foil, with a chemical conversion coated layer formed on the surface thereof, on a back bar made of a material having good electrical insulating property and heat resistance, arranging an electrically-conductive metal on the aluminum foil, bring first and second electrode tips into contact under pressure with the surface of the electrically-conductive metal with the electrode tips spaced from each other and then causing a welding current to flow between the first and second electrode tips, thereby conducting the series resistance welding of the aluminum foil to the electrically-conductive metal.