Sericulture/filature was a leading industry to contribute to Japanese economy in early twenty century. Silk mills have a key role of yarn reeling process and produce high quality silk from cocoon. Gunma Prefecture is called as a “Silk Country” resulting from both cocoon and raw silk production amount. Tomioka Silk Mill in Gu nma was inscribed as a World Cultural Heritage as the presence of reeling technologies. Most of the mills was closed during World War II, but after the war over 30 mills was quickly recovered with domestic market demands. However, the business was slowing down again due to business recession after oil shock and cheaper imported silk. The silk mills shut down year by year and at present only one silk mill is operating. The objectives of this research are to clarify (1) location of the mills, (2) current util ization of the sites, and (3) outcomes from the historical background of the mills. There are five kinds of the site utilization – public facilities, commercial complex, housing district, factories and open space. The major business owners tend to maintain the sites in case but mostly it is not easy to define a trace of silk mills there.