Kōtaku-ji, Buddhist temple in Tsuruoka, Japan

Kōtaku-ji is the head temple of the Haguro-san Shugen Hon-shū, a mountain ascetic order, in Tsuruoka, Yamagata Prefecture. Its mountain name is Haguro-san, and Shōzen-in serves as the main residence (honbō). The temple enshrines Dainichi Nyorai, Amida Nyorai and Kannon Bosatsu. The Shōzen-in Ōgon-dō, a hall dedicated to Kannon, is designated an Important Cultural Property.

Kōtaku-ji traces its founding to Prince Hachiko, son of Emperor Sushun, and served for centuries as a center of mountain worship and Shugendō for the Dewa Sanzan. Originally centered on Shingon Buddhism, it came under the Tendai school in the Edo period. In the early Meiji era it became a branch temple of Enryaku-ji, and in 1946 Shimazu Dendō established it as the head temple of the Haguro-san Shugen Hon-shū.

Kōtaku-ji belongs to the Haguro Shugendō Hon-shū, a school of mountain asceticism that follows neither the Shingon Tōzan-ha nor the Tendai Honzan-ha, joining older Shugendō practice with the local cult of Mount Gassan's ancestral spirits. Its defining rite is the Jikkai-gyō: the ascetic symbolically dies, passes through the ten realms of existence at training sites on the mountain, and is reborn into this world. This full ten-realm practice distinguishes it from the rites of the Dewa Sanzan Shrine, which are Shinto and more simplified.

Kōtaku-ji stands on Mount Haguro in Tsuruoka, with Shōzen-in serving as the main residence (honbō) of the Haguro Shugendō headquarters. The temple is the head temple of the Haguro Shugendō sect, so visitors should expect an active training site rather than a sightseeing circuit.

Kōtaku-ji belongs to the Haguro Shugendō Hon-shū, a school outside both the Shingon Tōzan-ha and Tendai Honzan-ha. Its defining practice is the Jikkai-gyō: the ascetic ritually dies and passes through ten realms, from hell to buddhahood, at training sites on the mountain before returning to this world. The Dewa Sanzan Shrine performs a simplified Shintō version.