ENIn order to quantify the degree of lexical divergence of the East Slavic languages, three fragments from the Kyiv chronicle of the early 12th-century The Tale of Bygone Years (Old Russian language) and three articles from the Statute of the Grand Duchy of Lithuania (Old Belarusian / Old Ukrainian language; printed edition of 1588 in Vilna) are compared with translations into modern East Slavic languages. It is shown that the divergence of related languages increases over time; therefore, in particular, modern equivalent East Slavic translations of the chronicle fragments are lexically closer to the original sources of the 12th century and to each other than are the translations of the articles of the Statute in relation to the original sources of 1588 and to each other. Of the three languages, Belarusian and Ukrainian are lexically closest to each other; by comparison, the pairs “Belarusian – Russian” and “Ukrainian – Russian” are at a much greater distance. Keywords: Tale of Bygone Years of the 12th century, Statute of the Grand Duchy of Lithuania 1588, Old Russian language, Old Belarusian (Old Ukrainian) language, Church Slavonicisms, Polonisms.