The present invention relates to a method for preparing a metallic membrane, more particularly to a method for preparing metallic membranes, which comprises dissolving a transition metal of Period 3 and its alloy particle powder and synthetic polymer in a fixed ratio; radiating or casting to prepare a membrane precursor; oxidizing the synthetic polymer on the membrane precursor under a mixed gaseous atmosphere of nitrogen and hydrogen; and sintering the membrane precursor at a predetermined temperature. The metallic membrane prepared by the process of the present invention has excellent mechanical and chemical properties and enables to maintain a relatively small pore size and high porocity than traditional membranes. Therefore, it is useful for water treatment.