Nagaoka Castle, Japanese castle in Nagaoka, Japan

Nagaoka Castle is a former Japanese fortress in Nagaoka now preserved as an archaeological site. Only foundation stones and reconstructed wall sections remain from the original structure, displayed in the local museum.

Hori Naoyori moved his seat from Zaōdo on the east bank of the Shinano River to higher ground on the west bank in 1616, starting Nagaoka Castle; he was transferred to Murakami in 1618 and Makino Tadanari completed it. The Makino held it until the Meiji Restoration. A 1728 fire burned most of it, restored only by 1754; the 1829 Sanjō earthquake wrecked most structures, and Boshin War fighting destroyed it in 1868.

The name Nagaoka comes from the castle town that grew around the new seat Hori Naoyori moved here in 1616. The Makino clan, lords of the 74,000-koku Nagaoka Domain, held the castle until the Meiji Restoration. Today the Honmaru site is Nagaoka Station, and place names such as Jōnaichō and the Ōteguchi station exit keep the castle's outline in the city.

The site sits just a three-minute walk from Nagaoka Station and is freely accessible. The nearby city museum displays original wall fragments and provides context about the former compound.

In 1954, while a underpass was being dug beneath Nagaoka Station, foundation stones of the castle's ramparts were found 4 m underground. They were not wall stones. Some were later set into the stone wall of the Nagaoka City Local History Museum on Mount Yūkyū, whose building is styled like a keep but has no connection to the castle.