In the summer of 1984, an assemblage of 358 bronze sword blades were found a few meters up a hill in the Kojindani area, Shimane prefecture, Japan. The sword blades, which all measure about 50 cm in length and weigh about 500 g, are of the Yayoi type and estimated to have been made in Japan some 1,800 years ago, after the style of Korean prototypes. They were laid in four rows on a square-shaped platform, covered with soil, and kept untouched until the present day. In July 1985, another group of Yayoi bronzes were excavated at a nearby location on the same hillside and consisted of six <i>dotaku</i> and 16 large bronze spearheads. Chemical examination of these bronzes was conducted using nondestructive methods. X-ray fluorescence analysis showed that the major components of the sword blades are copper, tin, and lead, which are common in Yayoi bronzes. X-ray diffraction revealed the presence of malachite, azurite, and cuprite in the surface layer of the sword blades, but no evidence was obtained of the existence of copper hydroxychloride. Lead isotope analysis of all the specimens brought some unexpected information not only on the material provenance but also on the location of casting and related processes in the case of the sword blades.