ln this article the writer discussed about the topography,geology,soil,current, climate, arable land, orangery and population of the oosima-gun in Yamaguti Prefecture. The Oosima-gun, generally speaking, has been blessed with the environmental factors、and has valued herself on her political and economical authority to a certain extent,though she has never secured any leadership not only in whole Japan but also in western Japan, but has been left in subordinate position. The writer is rather inclined to value the island lower as a sphere of modern life.