Ehime Prefecture (愛媛県, Ehime-ken; Japanese pronunciation: [eꜜ.çi.me, e.çi.meꜜ.keɴ]) is a prefecture of Japan located on the island of Shikoku. Ehime Prefecture has a population of 1,334,841 and a geographic area of 5,676 km² (2,191 sq mi). Ehime Prefecture borders Kagawa Prefecture to the northeast, Tokushima Prefecture to the east, and Kōchi Prefecture to the southeast. Ehime Prefecture Prefecture also borders Hiroshima Prefecture for 74 metres (243 ft) on Hyōtanjima.

Matsuyama is the capital and largest city of Ehime Prefecture and the largest city on Shikoku, with other major cities including Imabari, Niihama, and Saijō.

Notable past Ehime residents include three Nobel Prize winners: Kenzaburo Oe (1994 Nobel Prize in Literature), Shuji Nakamura (2014 Nobel Prize in Physics), and Syukuro Manabe (2021 Nobel Prize in Physics).

Until the Meiji Restoration, Ehime Prefecture was known as Iyo Province. Since before the Heian period, the area was dominated by fishermen and sailors who played an important role in defending Japan against pirates and Mongolian invasions.

After the Battle of Sekigahara, the Tokugawa shōgun gave the area to his allies, including Katō Yoshiaki who built Matsuyama Castle, forming the basis for the modern city of Matsuyama.

The name Ehime comes from the kuniumi part of the Kojiki where Iyo Province is mythologically named Ehime, "lovely princess".

In 2012, a research group from the University of Tokyo and Ehime University said they had discovered rare earth deposits in Matsuyama.

Located in the northwestern part of Shikoku, Ehime faces the Seto Inland Sea to the north and is bordered by Kagawa and Tokushima in the east and Kōchi in the south.