Western Belorussia or Western Belarus (Belarusian: Заходняя Беларусь, romanized: Zachodniaja Bielaruś; Polish: Zachodnia Białoruś; Russian: Западная Белоруссия, romanized: Zapadnaya Belorussiya) is a historical region of modern-day Belarus which belonged to the Second Polish Republic during the interwar period. For twenty years before the 1939 invasion of Poland, it was the northern part of the Polish Kresy macroregion. Following the end of World War II in Europe, most of Western Belorussia was ceded to the Soviet Union by the Allies, while some of it, including Białystok, was given to the Polish People's Republic. Until the dissolution of the Soviet Union in 1991, Western Belorussia formed the western part of the Byelorussian Soviet Socialist Republic (BSSR). Today, it constitutes the west of modern Belarus.

Created by the USSR after the conquest of Poland, the new western provinces of Byelorussian SSR acquired from Poland included Baranavichy, Belastok, Brest, Vileyka and the Pinsk Regions. They were reorganized one more time after the Soviet liberation of Belarus into the contemporary western provinces of Belarus which include all of Grodno and Brest voblasts, as well as parts of today's Minsk and Vitebsk voblasts. Vilnius was returned by the USSR to the Republic of Lithuania which soon after that became the Lithuanian SSR.