Traditionally, the existence of linguistic thought in the Old Belarusian written language is associated with handwritten and printed grammars, the practice of glosses and references. However, in addition to this, religious and polemical works of the late XVI – early XVII centuries provide rich material. The object of study in this article is parts of the works of Brest Synod by Piotr Skarga, The Apocrisis by Christopher Filalet, The Antirresis by Hypatius Potei, and The Palinody by Zachary Kopystensky, in which elements of linguistic research were identified. As a result of the description, comprehension and systematization of these parts, it has been established that they are most often associated with the practice of translation: individual words and expressions are explained in the margins, a textual comparison of the original source and the translation is carried out, the semantic, grammatical and word-formation aspects of the text being translated and already translated text are touched upon. The analysis of the system of names of special concepts used in the works under consideration revealed both linguistic terms already established in the scientific discourse of that time, dating back to ancient Greek and Latin traditions (антонνмія, арѳра, арѳронъ, женский родъ, имя, мѣстоимение, началное имя, сенсъ, синонима, члонки грамматичныи /antonymy, category, арѳронъ, feminine gender, name, pronoun, initial name, sense, synonym, grammatical parts), and peculiar preterms (прекладанье, прекладане, перекладъ, переложити /translation, translate/, etc.), some of which express their proximity to the Polish-speaking tradition. Among other results of the conducted research, there is the revealed connection of the text of The Apocrisis by Christopher Filаlet with the text of the polemical work of the Anglican Bishop of Salisbury John Jewel. The text excerpts with elements of linguistic research, considered in this article, allow us to link the origins of the Russian science of the theory and practice of translation with Old Belarusian religious and polemical works and indicate a high level of development of philological thinking at that time.