Oust-Kout (in Russian: Усть-Кут) is a city of the Oblast d' Irkoutsk, in Russia. It is located on the Lena, to 500 km in the north of Irkoutsk. Its population rose with: 54600 inhabitants in 2003.

In 1631, the Ataman Cosaque Ivan Galkine built there a fort, which is at the origin of the current city. The locality accepted the statute of city in 1954.

Leon Trotsky was exiled in Oust-Kout in 1900.