The paper examines newly discovered lexical substitutions in the Life of Saint Theodore the Studite, edited by Nil Sorsky. This Life originally belongs to the ancient translations from Greek made by South Slavic scribes in the territory of Old Rus’. It is shown that, in the Life edited by Nil, among the majority of lexical substitutions, which are freely differentiated into groups, there are examples of lexical improvements that require particular consideration. Such exclusive substitutions include corrections of translator’s errors based solely on the Church Slavonic context of the extract (изложенїе – низложенїе), the introduction of Slavic explanations to Greek words preserved in the text (ѥпитимиꙗ – запрѣщениѥ) in accordance with the traditions of the Athos-Tyrnovo school of book reading, as well as the replacement of lexical and semantic archaisms with the synonyms commonly used in the 15th – 16th century texts (позоръ – позорище, притъча – ѡбразъ). It has been established that a striking feature of the lexical revisions carried out by Nil is the desire to adapt the original text to the perception of a scribe of the late 15th – early 16th centuries. The discovered lexical substitutions enable the conclusion that the Sorsky ascetic, undoubtedly guided by the lexical norms of the new Svyatogorsk translations and taking into account the development of the Middle Russian variant of Church Slavonic, approached the correction of each lexeme individually.