An objective of the present invention is to provide a method for producing a rare earth metal-based permanent magnet having an Al film containing Mg, which exhibits an excellent salt water resistance. The present invention, which is to accomplish the objective, is a method for producing a rare earth metal-based permanent magnet having formed on the surface thereof an Al film containing Mg by a vapor deposition, characterized in that the production method comprises, in the case of cooling the magnet from a high temperature of 160° C. or higher after the completion of the vapor deposition step inside the treating chamber of a deposition apparatus, rapidly cooling down the magnet at a cooling rate of 10° C./min or higher until the temperature of the magnet reaches at least 60° C.