The aim of this article is to show the development of linguistic thought at Vilnius University in the period 1805–1832 on the basis of the unpublished doctor’s dissertation The Essays on the History of Slavic Philology at Vilnius University at the Beginning of the 19th Century [Очерки по истории славянской филологии в Вильнюсском университете в начале XIX века] of Anna Kaupuż (1924–1994), a good archive expert. Following the materials found in the Lithuanian, Polish and Russian archives, the researcher reveals the place of linguistic issues in the didactics and scholarly interests of Vilnius University professors during this period of the development of historical-comparative linguistics. The research activities of Ivan Cherniavsky (1768–1822), Eusebius Slovacki (1773–1814), Leon Borovsky (1784–1846), and Ivan Loboiko (1786–1864), professors who held positions in the two departments, that is, in the Department of Russian Language and Literature and the Department of Rhetoric and Poetry, during the period in question, are examined in detail. The research allows to conclude that linguistic views of the afore-mentioned researchers were fully in line with the spirit of the period – their worldview was still influenced by classicist thinking but the comparativist ideas had reached the University, research in the Lithuanian language started, and the works in the field of dialectology were published. Thanks to I. Loboiko, Vilnius University became one of the few academic centres in Europe of that time, where comparative grammar of Slavic languages was taught.