Ōtaki Castle, Japanese castle in Otaki, Japan.

Ōtaki Castle is a flatland-mountain castle in Ōtaki, Chiba Prefecture, originally called Odaki Castle. The current keep is a three-story, four-floor reinforced-concrete reconstruction built in 1975 on the main bailey site, which was leveled in 1871. Earthworks remain near the main bailey, a moat trace near the Ōtemon gate, and a large well in the ninomaru.

The Satomi clan built the first fortress here in the early 16th century when the region was under their control. Honda Tadakatsu rebuilt the site starting in 1590 under orders from Tokugawa Ieyasu and reinforced its strategic importance.

The sword exhibition inside displays Japanese blades from different eras, arranged carefully in lit cases. Visitors also find traditional armor and everyday objects that show the lives of samurai and their families during the Edo period.

The reconstructed keep stands on the Honmaru site, a Chiba Prefecture historic site, with earthworks nearby and a moat trace by the Ōtemon gate. The Ōi well in the Ni-no-maru measures 17 metres around. The castle museum has been closed since 27 December 2021, and the site is to become a town-run museum.

The keep standing today is a 1975 reconstruction in reinforced concrete, designed by architectural historian Fujioka Michio and completed on 10 September 1975. It was raised from a three-storey keep drawing copied in the Tenpō era, not from any surviving original plan. Since 2021 the museum inside has been closed long-term, with the facility due to pass from the prefecture to Ōtaki Town.