Sericulture/filature was a leading industry to contribute to Japanese economy in early twentieth century. Silk mills have a key role for yarn reeling process and produce high quality silk from cocoon. Most of the mills were closed during World War II, but after the war over 300 mills quickly recovered with domestic market demands. Katakura and Gunze were two major silk yarn manufacturers. Due to business recession, their silk mills shut down year by year and they were replaced by other factories or shopping moles. The objectives of this research are to clarify changes or business transition of the site utilization while comparing the two manufacturers. Katakura shifts from silk yarn reeling to commercial developer business by use of their sites having enough land space where mostly located close to major railway stations. Shopping moles are managed by Katakura at the sites as their real-estate asset. Gunze shifts to innerwear manufacturer in earlier stage. They took a position of major player as apparel business by use of silk mills site where mostly being unsuitable to commercial zone. Gunze increases diversification of their business to commercial developer and medical materials depending on each site location.