The Yosan Line is the principal railway line on the island of Shikoku in Japan, connecting the major cities of Shikoku, and via the Honshi-Bisan Line, with Honshu. It is operated by the Shikoku Railway Company, and is aligned approximately parallel with the Inland Sea coast, connecting the prefectural capitals of Takamatsu and Matsuyama and continuing on to Uwajima. The name of the line comes from Iyo (伊予) and Sanuki (讃岐), the old names of Ehime and Kagawa, respectively.

Shikoku , Japanese pronunciation: [ɕikokɯ] is the smallest of the four main islands of Japan. It is 300 km or 186.4 mi long and between 50 and 150 km or 31.1 and 93.2 mi at its widest. It has a population of 3.8 million, the least populated out of Japan's four main islands. It is south of Honshu and northeast of Kyushu. Shikoku's ancient names include Iyo-no-futana-shima (伊予之二名島), Iyo-shima (伊予島), and Futana-shima (二名島), and its current name refers to the four former provinces that make up the island: Awa, Tosa, Sanuki, and Iyo.