Kosh-Agach (; , Koà Â-Agaà Â; , QosaÃÂaà Â) is a rural locality (a selo) and the administrative center of Kosh-Agachsky District of the Altai Republic, Russia. Population:
According to the Köppen Climate Classification, Kosh-Agach has a subarctic climate (Dwc), bordering upon a cold arid climate (BWk). The village experiences short, mild summers and long, frigid and extremely dry winters. It is one of the driest places in Russia with annual precipitation just , and just from September to May.
The Baratal limestone, potentially the oldest atoll in the world, was found here.