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Some characteristic changes of ultra-fine powders obtained by a recently developed dry grinding system called UMF were introduced together with the performance of the grinding system. UMF has made it possible to grind not only the general minerals but also some hard substances like zirconium oxide, silicon nitride etc. down to submicron powder in dry condition. In addition, the grinding capacity was greater than that expected from conventional mills taking into account product fineness. The differences of some powder characteristics between the ground product and the raw material were confirmed, using an electron microscope, thermogravimetry, differential thermal analysis and X-ray diffraction analysis for several materials including calcium carbonate, mica, barium titanate and so on.