The metallurgy of historic melee weapons (swords, in particular) is one of the most significant topics in archaeometallurgy because these objects were manufactured intuitively for a thousand years using the highest quality materials and the most advanced technology of their age. They remain among the best steel ever made. Japanese steel arms represent, probably, the most important topic in this field of historical metallurgy. We propose to analyse, on the INES diffactometer, four ancient Japanese swords pertaining to a private collector and renowned among the best ancient Japanese swords present in Europe and cited in several catalogues and bulletins of the European branch of the Society for the Preservation of Japanese Swords. We want to measure the composition and micro structural properties in different selected cross sections of the blades,