Agin-Buryat Autonomous Area (əgyēn'bo͝oryät`) or
Aga Buryat (äg`ə bo͝oryät`), former administrative division, S Siberian Russia, in what is now the Transbaykal Territory. Aginskoye was the capital. Formed in 1937, the area followed the Onon River. Buryats, Buddhist descendants of the Mongols, made up about 54% of the area's population. In 2008 the autonomous area was merged with the surrounding Chita region to form the Transbaykal Territory.