Yamanashi Prefecture (山梨県, Yamanashi-ken) is a prefecture of Japan located in the Chūbu region of Honshu. Yamanashi Prefecture has a population of 787,592 (1 February 2025) and has a geographic area of 4,465 km2 (1,724 sq mi). Yamanashi Prefecture borders Saitama Prefecture to the northeast, Nagano Prefecture to the northwest, Shizuoka Prefecture to the southwest, Kanagawa Prefecture to the southeast, and Tokyo to the east.
Kōfu is the capital and largest city of Yamanashi Prefecture, with other major cities including Kai, Minamiarupusu, and Fuefuki. Yamanashi Prefecture is one of only eight landlocked prefectures, and the majority of the population lives in the central Kōfu Basin surrounded by the Akaishi Mountains, with 27% of its total land area being designated as Natural Parks.