The Socialist Soviet Republic of Byelorussia or Soviet Socialist Republic of Belarus (SSRB; Belarusian: Савецкая Сацыялістычная Рэспубліка Беларусь, Savieckaja Sacyjalistyčnaja Respublika Biełaruś; Russian: Социалистическая Советская Республика Белоруссия / ССРБ, Socialističeskaja Sovetskaja Respublika Belorussija / SSRB) was an early republic in the historical territory of Belarus after the collapse of the Russian Empire as a result of the October Revolution.
Bolsheviks first established the Republic on January 1, 1919 in Smolensk when the Red Army entered Belarusian lands following the retreating German army, which had been occupying the territory as a consequence of World War I. The SSRB replaced the Belarusian People's Republic, and consisted of the governorates of Smolensk, Vitebsk, Mogilev, Minsk, Grodno, and Vilna.
It was considered by Bolsheviks to be a buffer republic. In a month it was disbanded. The Smolensk, Vitebsk and Mogilev provinces were included in the Russian Soviet Federative Socialist Republic (RSFSR), and the remainder formed another buffer republic, the Lithuanian–Belorussian Soviet Socialist Republic (Litbel).
The republic was re-established under the same name on July 31, 1920. However, in traditional Soviet historiography it has been referred to as the Byelorussian Soviet Socialist Republic (BSSR), its name after the incorporation into the Soviet Union in 1922.