Kōchi Prefecture (高知県, Kōchi-ken; Japanese pronunciation: [koꜜː.tɕi, koː.tɕi̥ꜜ.keɴ], locally [koː.tɕi]) is a prefecture of Japan located on the island of Shikoku. Kōchi Prefecture has a population of 669,516 (1 April 2023) and has a geographic area of 7,103 km² (2,742 sq mi). Kōchi Prefecture borders Ehime Prefecture to the northwest and Tokushima Prefecture to the northeast.

Kōchi is the capital and largest city of Kōchi Prefecture, with other major cities including Nankoku, Shimanto, and Kōnan. Kōchi Prefecture is located on Japan's Pacific coast surrounding a large bay in the south of Shikoku, with the southernmost point of the island located at Cape Ashizuri in Tosashimizu. Kōchi Prefecture is home to Kōchi Castle, considered the most intact Japanese castle, and the Shimanto River, one of the few undammed rivers in Japan.

In the Kujiki, first recorded governments in Kōchi Prefecture were Hata (in the west) and Tosa (in the center). Hata was established first, so it is thought that it had more influence and contact with the Yamato court. Written records from this time period are sparse, however it is believed that the first governors of Hata and Tosa were from the Kamo clan based in modern Osaka.

In the Nihon Shoki, the first report from an official in the Kōchi region described the damages caused by the 684 Hakuhō earthquake. From this report, it can be inferred that by 684 at the latest, the Tosa Province (a predecessor to modern-day Kōchi Prefecture) had been established. The first report from a named official was written by Hiketa no Mushiro in 743.

Up until the Genpei War, 106 governors were appointed to govern the Tosa Province. Eventually, like many other provinces Tosa also was appointed absentee governors, given additional rights, and began amassing wealth. Due to being located far from the capital, many prisoners were exiled to the Tosa Province.

The Kamakura Shogunate was established at the end of the 12th century. Since Tosa Province was allied to the winning Minamoto Clan in the Genpei War, it quickly fell under the influence of the shogunate. Kajiwara Tomokage was appointed as the first military governor of the Tosa Province. Eventually, the Hōjō Clan began serving as the military governor for the province.

After the fall of the Kamakura Shoguante, Ashikaga Takauji was defeated in battle and forced to retreat to Kyushu. Shikoku Island later fell under the control of the Hosokawa Clan.

Kōchi Prefecture was historically known as Tosa Province and was controlled by the Chōsokabe clan in the Sengoku period and the Yamauchi clan during the Edo period.