From the Wikipedia page 
The Buryat Autonomous Soviet Socialist Republic (Buryat: Буряадай Автономито Совет Социалис Республика; Russian: Бурятская Автономная Советская Социалистическая Республика) was an Autonomous Soviet Socialist Republic of the Russian SFSR in the Soviet Union.
In 1923, the republic was created with the name Buryat-Mongol Autonomous Soviet Socialist Republic; its predecessor was the Buryat-Mongol Autonomous Oblast. In 1958, the name "Mongol" was removed from the name of the republic. The Buryat ASSR declared its sovereignty in 1990 and adopted the name Republic of Buryatia in 1992. However, it remained an autonomous republic within the Russian Federation.