Unsai-ji, Buddhist temple in Ōshū, Japan.

Unsai-ji is a Sōtō-shū temple on Mount Myōkō in the Hirabayashi district of Koromogawa, Ōshū, Iwate Prefecture. Its main hall was rebuilt in July 2010 after a fire on 6 August 2008 destroyed the previous hall, the ihai hall and a residential wing. The temple keeps memorial tablets (ihai) for Minamoto no Yoshitsune and his wife, the Kita no Kata.

Founded as the Tendai temple Baisei-ji on Gogyoku-zan, it was revived in 1187 by the monk Minbukyō Zenji Yoranen, who stayed behind when Minamoto no Yoshitsune fled to Hiraizumi. After Yoshitsune and his wife died at Koromo River in 1189, their bodies were brought here and Yoranen installed ihai tablets for them. The temple converted to Sōtō-shū in 1473, was rebuilt under the Ashina clan in the Edo period, and lost its main hall and ihai hall to fire in 2008; the main hall was rebuilt in 2010.

The temple keeps the memorial tablets (ihai) of Minamoto no Yoshitsune and his wife, installed by the monk Raisan after Yoshitsune's death at the Koromo River residence in 1189. The temple was rebuilt in the Sōtō-shū school in 1473 and later restored under the patronage of the Ashina clan in the Edo period.

Unsai-ji stands in the Zhangshan area of Koromogawa, Ōshū, Iwate Prefecture, in the hills north of the Kitakami River. The temple is reached by road from the Koromogawa district; the nearest rail access is via the Tōhoku Shinkansen corridor and connecting regional lines. The main hall was rebuilt after the 2008 fire, so check locally before visiting.

In 1189, after Minamoto no Yoshitsune killed himself and his family at the Koromo River residence, his body was said to be carried to this temple, where the monk Ranyo installed memorial tablets for Yoshitsune and his wife. A fire on 6 August 2008 burned the main hall, the tablet hall and a residential wing, destroying the main image of Fudo Myoo and those tablets; the main hall was rebuilt in July 2010.