To provide a method for producing an Fe-Ni series or Fe-Ni-Co series alloy thin sheet excellent in etching properties and to obtain a thin sheet for a shadow mask excellent in various characteristics and a shadow mask.

In the method for producing a low thermal expansion alloy thin sheet of an Fe-Ni series containing, by mass, 30 to 50% Ni or of an Fe-Ni- Co series containing ≤7% Co and 27 to 40% (Ni+Co), at the time of forming a laminated and solidified ingot in which the angle between the substantial solidifying direction and the growing direction of dendrite is controlled to 50°C or more, preferably to 70°C or more on the acute angle side into a thin sheet, blooming forging is performed in such a manner that the substantial solidifying direction comes to the sheet thickness direction of the thin sheet, and hot rolling and cold rolling are performed.