Abstract: According to the present invention, a metal sheet is prepared by subjecting an Al slab, containing at least one element capable of peritectic reaction with Al, such as Ti, Zr and Mo, the amount of the element incorporated in the slab being 0.05 to 0.4% by weight when one element is incorporated and when two or more elements are incorporated, the amount of at least one element incorporated therein being 0.05 to 0.4% by weight and the total amount of the elements incorporated being not higher than 0.5% by weight, to a soaking heat treatment, hot-rolling the slab and then cold-rolling the hot-rolled slab. According to the present invention, the properties required for such metal sheet, namely the strength and formability, can be remarkably improved, and by the hardening treatment, the adherence between fins and tubes can be improved and the heat transfer efficiency can be remarkably elevated in the heat exchangers. Thus, according to the present invention, practically applicable hard thin fins can be provided.