In manufacturing a corrosion-resistant metallic porous member having high Cr content by diffusion process in which the material is heat-treated, a plurality of heat cycles are used to achieve uniform Cr content in the thickness direction.Metallic porous body of Ni, Fe, Ni--Cr or Fe--Cr is buried in a powder of Al, Cr and NH.sub.4 Cl. Inert gas such as Ar and H.sub.2 is introduced and the porous body is heat treated at 800.degree.-1100.degree. C. In the heat treatment, at least two temperature-increase and temperature-decrease steps are included.