A method of compression molding powders of metals, ceramics and the like. A thin rubber bag is adhered to the inside of a cavity formed within a permeable mold support so as to define a mold therein and the bag is packed with a raw material powder. The powder in the bag is evacuated to a degree of vacuum to compactly compress it and the rubber bag is sealed. In this condition, the compressed powder is removed from the support and compression molded to a higher degree of denseness by the CIP process. The inflation adhesion of the rubber bag to the inside of the support cavity is effected by reducing the pressure outside the permeable support.