The state and functioning of languages in the state is influenced by the language policy, which is an integral part of the national policy in multinational states. The experience of language building in Belarus demonstrates a situation that is unique for the post-Soviet countries, when two state languages, Belarusian and Russian, are used in conditions of diglossia. However, this specific linguistic situation is the result of a fairly long period of the Belarusian language development and the fact that modern Belarusian territories were part of different states: the Grand Duchy of Lithuania, Polish-Lithuanian Commonwealth and the USSR. The author analyzes the specific language situation in the Republic of Belarus and focuses on the historical analysis of the previous experience of language policy during the USSR period. The approaches and results of Belarusianization in the field of language policy are described in the article. The author considers the national and cultural policy in the BSSR as part of the Soviet policy of “indigenization”, but with goals and conditions specific to the Slavic peoples. This policy and its further transformation significantly influenced the functioning of Belarusian not only for all subsequent Soviet years, but also has a considerable impact today. In fact, the existence of two spelling norms of the modern Belarusian language and a mixed version of the Belarusian-Russian language, hinders the active development of the national language of Belarus. Despite the fact that both languages, Belarusian and Russian, have equal rights in the Republic of Belarus under the Constitution, both in official and in everyday communication, citizens of the country prefer Russian. At the same time, the Belarusian folk dialects and the variability of the Belarusian literary language have a negative impact on the further development and status of the national language.