PURPOSE: To provide a joined part having sufficient joining strength by arranging an anode electrode tip 3 and a cathode electrode tip 4 of a DC resistance spot welding machine on an aluminum alloy sheet and a steel sheet, respectively to perform spot welding.

CONSTITUTION: The aluminum alloy sheet 2 and the steel sheet (mild steel sheet) 1 are superposed on each other, the anode electrode tip 3 and the cathode electrode tip 4 are abutted on the aluminum alloy sheet 2 side and the steel sheet 1 side, respectively and spot welding is performed under specified conditions by using the DC resistance spot welding machine. A nugget 5 is formed on the joined interface between the steel sheet 1 and the aluminum alloy sheet 2 on an cross section of a cut part of an obtained test piece. Consequently, the steel sheet and the aluminum alloy sheet are subjected to spot welding and the joined part having the sufficient joining strength can be formed. This welding method is useful in welding of the steel sheet and the aluminum alloy sheet required at the diversified manufacturing stages of automobiles.