The Russian language in Belarus is one of the two official languages (the other being Belarusian). Being dominant in the media, education and other areas of public life, Russian is de facto the main language of the country.
After 1995
In 1995, according to the results of the 1995 Belarusian Referendum, the Russian language was declared the second official language. According to the Belarus Census (2009), 41.5% of the Belarusian population declared Russian as their mother language and 70.2% declared Russian "the language spoken at home" (the second language-related question of the Census).
References
Russian language in Belarus Wikipedia(Text) CC BY-SA