Oki (隠岐国; -no kuni) was an old province of Japan which consisted of Oki Islands in the Sea of Japan, located off the coast of Izumo and Hoki provinces.

The Oki Islands consist of two relatively big islands and some smaller ones. The capital of the province was settled in Saigo city today, but the relics of the provincial capital have not been found. Kokubunji, founded in the Nara period under the order of the Emperor Shomu, remains today in Saigo town. It was one of exile sites, and the Emperor Go-Toba and Go-Daigo exiled in Oki Proivince.

From the Kamakura period Oki Province was governed by the shugo of Izuo province mostly. In the Muromachi period, Sasaki clan , Yamana clan and Kyogoku clan governed the province successively. In the Sengoku period the Amako clan held this province. After they declined and the Tokugawa Shogunate arose, the Shogunate determined the province the dominion of the shogun and had Matsue han, a daimyo belonging to Matsudaira clan , relatives of the Shogun, govern it. The rice production from Oki province per year was calculated at five thousand koku.

Today it is Oki District, Shimane, a part of Shimane prefecture.