This article is devoted to theoretical and methodological problems of making a dictionary of the living Belarusian language in the 20th years of twentieth century in comparison with the most important Russian, Polish, Czech, Serbian and Ukrainian dictionaries. The special attention has been paid to works of Belarusian linguists which rethinking and reworking experience of other Slavic counterparts offered their own lexicographical installation of the methodological support of works as well as implemented them. Publications of regulations and programs, preparation of regional dictionaries, field collection of dictionary materials by forces of the literate part of population of the Republic have been elucidated, too. Also theoretical foundations of the dictionary based on the Belarusian living language encompassed territorial boundaries of ethnographic Belarus have been shown. They are chronologically limited to the second half of nineteenth century and the first quarter of the twentieth century. The goal of the dictionary was to show the lexical richness of the Belarusian language, stylistically processed vernacular, introducing a significant part of specialized vocabulary. Thereby it proves the uniqueness of the Belarusian language and extracts tokens from artistic, journalistic and professional literature. This extraction had a critical nature. So the usage labels have been not introduced into the entries in contrast to the mandatory examples from literature and compulsory linguistic passports. At the same time the criteria for inclusion into the dictionary of loan words, neologisms and special vocabulary were rather vague.