Kosh-Agach (Russian: Кош-Ага́ч; Altay: Кӧжӧӧ-Агаш,[2] Koş-Agaş; Kazakh: Қосағаш, Qosağaş) is a rural locality (a selo) and the administrative center of Kosh-Agachsky District of the Altai Republic, Russia.

Population: 7,900 (2010 Census);[4] 5,701 (2002 Census);[8] 3,501 (1989 Soviet census).

[9] According to the Köppen Climate Classification, Kosh-Agach has a cold desert climate (BWk).

It is one of the driest places in Russia with annual precipitation just 124 mm.

The Baratal limestone, potentially the oldest atoll in the world, was found here.