Architectural preservation in Japan is discussed through the study and observation of Gekko-den pavilion at Gokoku-ji Temple in Central Tokyo. Gekko-den’s importance lies in its affiliation with Onjo-ji Temple, founded in early Heian Period, 672, a designated National Treasure of Japan, and head temple of the Tendaijimon Buddhist sect. Preservation of Gekko-den commenced in November 2008, and will continue through to October 2013. Historical analysis and overview of Cultural Property definition in Japan and the legal system and administration that functions to oversee the protection and preservation of the cultural properties are examined in detail.