Hayashi Castle, Hill castle in Matsumoto, Japan

Hayashi Castle is a yamashiro-style fortification in southeastern Matsumoto, Nagano Prefecture, made up of two separate enclosures on facing ridges. The northern ridge holds the Hayashi Large Castle, a flat summit of about 100 square metres where the Ogasawara lords resided, ringed by earthen walls with terraces in front and dry moats behind. The Hayashi Small Castle lies roughly 500 metres south on the opposite ridge, the main defensive centre, with several terraced levels, stone ramparts and dry moats. Only stairs, a well and low stone walls remain.

Hayashi Castle was built in 1459 by Ogasawara Kiyomune, replacing the smaller Igawa Castle as the Ogasawara clan headquarters. Ogasawara Nagatoki lost the province after defeat at Shiojiritoge Pass in 1548, and on 15 July 1550 Takeda Shingen took Hayashi Castle in a single night. The Takeda kept it to guard their rear; the Ogasawara returned after 1582 but left Shinano in 1590.

The ruins lie in a valley between two ridges: the northern Hayashi Large Castle held the Ogasawara lords' residences, while the southern Hayashi Small Castle, about 500 metres away, was the main defensive centre. The small castle's name in Japanese is 林小城, and the large one 林大城. Visitors today find only stairs, a well and low stone walls.

The ruins lie on two ridges separated by a small valley, about 500 metres apart, in the southeast of Matsumoto. A walking path, the Higashijōyama promenade, is laid out around the Hayashi Large Castle on the northern ridge. Little survives beyond stairs, a well and low stone walls, so footing is uneven.

The smaller southern fort, Hayashi Small Castle, was long thought older than the main castle, but its complex layout suggests it was built later. It sits about 500 meters from the large castle, across the Osako settlement, and served as the main defensive center with terraces, stone ramparts and dry moats.