Tsukinasi Site, a low wetland site of the Yayoi period (300～200 B.C.-A.D. 200～300), is located on the riverbed of Yabi River in the Oki Islands.
　This site was discovered in 1966, and many unglazed Yayoi earthenware, stone implements, and wooden tools for cultivation were excavated. This site dates back to the end of the early phase or the beginning of the middle phase of the Yayoi period, and extends to the latter phase of the Yayoi period.
　Tsukinashi Site is positioned at a place below 0 meters above sea level, therefore indicating that the water sea level during the Yayoi period was lower than it is today. This is an important Point beyond considering the Yayoi period of the Oki Islands. In the future, if there are more investigations on the wetland site of the Oki Islands, then it could be possible to restore the ancient environment.