Château de Kanayamajo, Mountain castle in Marumori, Japan

Kanayama Castle was a hilltop fortress on Mount Kanayama with multiple defensive levels, stone walls, and bastions spread across different elevations. The ruins today still display several restored positions and fortifications that can be traced on foot.

Kanayama Castle was built around 1564–1565 by Ido-gawa Shōgen and Fujihashi Taneyasu, retainers of the Sōma clan, on Mount Odate (117 m) in Marumori. The Date and Sōma fought over it, and in 1581 Date Masamune made his first campaign there; by 1584 it was in Date hands and granted to Nakajima Munemoto for 2,000 koku. Under the Edo-period one-castle-per-domain rule it became Kanayama Yōgai, where the Nakajima family resided until the Meiji Restoration.

The castle's name is also written as Neyushi-jō or Gayū-jō, "the reclining ox castle", after the shape of the ridge on Mount Odate. After the 1615 one-castle-per-province decree it was kept as one of the Sendai domain's 21 yōgai forts and called Kanayama yōgai, where the Nakajima family lived until the Meiji Restoration.

The castle ruins are accessible via hiking paths that lead to various archaeological sites and pass by several restored positions. Visitors should wear proper footwear and allow enough time, as the paths are steep and uneven.

The honmaru keep site holds stone walls built around 1588 (Tenshō 16), which still stand on the summit of Mount Odate, 117 m above sea level. The castle is also called Neushi-jō or Gagyū-jō, "sleeping ox castle", after the shape of the hill.