Château d'Ishihamashiro, Japanese castle in Tokyo, Japan

Ishihamashiro was a medieval castle in Musashi Province whose exact site is disputed: candidates are around Asakusa 7-chome in Taito Ward or Minami-Senju 3-chome in Arakawa Ward. No ruins survive, as the flow of the Sumida River and later urbanization altered the terrain. The Taito theory places it near Honryū-in (Matsuchiyama Shōden), while the Arakawa theory places it near Ishihama Shrine.

The castle's founding date is unknown; in the Middle Ages the Ishihama clan, related to the Edo clan, was based here. In 1352 Ashikaga Takauji, pursued by Nitta Yoshioki, was received at this spot by the Musashi Ikki and repelled the pursuit. In the mid-Muromachi period Chiba Sanezane, driven from Shimōsa, made the castle his base as the Musashi Chiba clan. It fell with the Hōjō in Toyotomi Hideyoshi's 1590 Odawara campaign.

The name Ishihama comes from the old right-bank district of the Sumida River north of Asakusa, where the Sumida ferry linked Musashi and Shimōsa provinces. The castle is tied to the Musashi Chiba clan, whose head Chiba Sanehisa took refuge here after being driven from Shimōsa. The site is remembered in Kyokutei Bakin's novel Nansō Satomi Hakkenden.

No castle remains stand; the site is identified with the area around Ishihama Shrine in Minami-Senju 3-chome, Arakawa, where Tokyo's buried cultural property map marks the castle grounds slightly north of the shrine. South of the shrine lies Ishihama Castle Ruins Park (Minami-Senju 3-chome Park). The shrine is a short walk from Minami-Senju Station.

No trace of the castle survives, and even its location is disputed: one theory places it near Honryū-in (Matsuchiyama Shōden) in Asakusa, the other near Ishihama Shrine in Minami-Senju, where the shrine's priests were long hereditary members of the Kaburagi branch of the Chiba clan. Tokyo's buried cultural property map marks the site just north of Ishihama Shrine, and Ishihama Castle Ruins Park (Minami-Senju 3-chome Park) lies south of it.