| Conventional Long Name: | Socialist Soviet Republic of Byelorussia |
| Status: | Puppet/Buffer State of Soviet Russia |
| Date Start: | 1 January |
| Year Start: | 1919 |
| Year End: | 1919 |
| Date End: | February |
| Demonym: | Belarusian/Byelorussian |
| Government Type: | Soviet Republic |
| Life Span: | 1919 |
| Today: | Belarus |
| P1: | Belarusian People's Republic |
| Flag P1: | Flag of Belarus (1918, 1991–1995).svg |
| S1: | Socialist Soviet Republic of Lithuania and Belorussia |
| Flag S1: | Flag of the Lithuanian-Byelorussian SSR.svg |
The Socialist Soviet Republic of Byelorussia (SSRB; Belarusian: Сацыялістычная Савецкая Рэспубліка Беларусь|Sacyjalistyčnaja Savieckaja Respublika Biełaruś; Russian: Социалистическая Советская Республика Белоруссия / ССРБ|Sotsialisticheskaya Sovetskaya Respublika Belorussiya / SSRB) was an early republic in the historical territory of Belarus for only one month in 1919 after the collapse of the Russian Empire as a result of the October Revolution.
Bolsheviks first established the Republic on 1 January 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).
See main article: Byelorussian Soviet Socialist Republic. The republic was re-established under the same name on 31 July 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.