<p>The method for preparing a gaseous metallic fluoride is here disclosed which comprises reacting a metal or its oxide with a fluorine gas or nitrogen trifluoride gas, the aforesaid method being characterized by comprising the steps of mixing the metal or its oxide with a molding auxiliary comprising a solid metallic fluoride which does not react with fluorine and nitrogen trifluoride; molding the resulting mixture under pressure; and contacting the molded pieces with the fluorine gas or nitrogen trifluoride gas, while the molded pieces are heated.</p>
