Fukusumi Nakasada Castles, Mountain fortress in Tenri, Japan.

Fukusumi Nakasada Castle is a hilltop castle (hirayamajiro) in Fukusumi, Tenri, Nara Prefecture. Its main enclosure has a flat northern half resembling a square residence, surrounded by a 3 m high, 7 m wide earthen rampart with a projecting corner (ori) at its western end. Two attached enclosures lie to the southeast, and dry moats and a buried horizontal moat remain.

The name Fukusumi Castle first appears in 1434 alongside Tsutsui Castle in the records of Kōfuku-ji's Kensei-in. During the Ōnin War, forces of the Fukusumi and Tsutsui clans were stationed there; by 1475 the site was called Fukusumi Yakata and by 1481 Fukusumi Castle, suggesting a shift from residence to fortification. In 1569 Tsutsui Junkei fled to Fukusumi after Matsunaga Hisahide took Tsutsui Castle, and in 1570 Matsunaga's army attacked; Fukusumi Nakasada Castle's layout indicates Tsutsui involvement in its construction or renovation.

The castle takes its name from the Fukusumi clan, local governors who held the ritual rights of the Himuro shrine and passed the castle to the Tsutsui family when Tsutsui Jun'ei's elder brother Daitō inherited the Fukusumi line. Two castles stand in Fukusumi: Inoichi is considered the new castle, Nakasada the old one.

The site is reached by train to Tenri Station (JR Sakurai Line or Kintetsu Tenri Line), then Nara Kotsu bus route 21 to the Fukusumi stop, about 10 minutes on foot. By car, take National Route 25 from the Fukusumi interchange of the Meihan Expressway; parking for worshippers is available at the Godai Myoo shrine. The castle is now woodland, and the path between the main enclosure and the southeastern bailey is a later cut, not an original route.

The main enclosure's northern earthwork, 3 m high and about 7 m wide, ends in a westward projection called an ori, built so defenders could raise a tower and shoot sideways at attackers climbing from the north. Below it lies a moat cut, and the eastern side continues as a vertical trench, now buried.