The article presents the analysis of the collection of letters of the famous Ukrainian dramatist Mykola Kulish, representative of the generation Executed Renaissance. The writer’s correspondence is analysed as a component of his artistic heritage. The accent is made on the importance of studies of the writer’s correspondence, and the writer is seen as a representative of the inner world and the emotional and mental state of the word master, as it is exactly in the private correspondence that the author can be seen both as a writer and an ordinary person with his achievements, problems, and troubles. The article deals with the linguistic units – words, collocations, and sentences –that were used by M. Kulish in his correspondence with his colleagues in writing as indicators of his emotional and mental state. It was discovered what emotional background the lettеrs to his brothers in pen have, especially those written to I. Dniprovkyi, as well the reasons for his state of mind that defines the choice of linguistics means for its expression. M. Kulish’s letters contain his aesthetic principles of literary art, standpoints regarding his contemporary literature, evaluation of his own texts and the works of other authors. At the same time the writer appears before the reader as an ordinary person, exhausted by not being particularly healthy, by impecuniosity, provincial life and hard work in the institution of public and social education which is quite often greatly bureaucratised. It was found out that the inner state of Mykola Khvyliovyi is represented by means of lexical and phraseological groups with various semantic and stylistic, in particular vernacular colloquialisms, including the pejoratives, obsolete words from the ancient Slavonic language, cliché, ideologemes, some author’s neologisms. The role of phraseological units of different types such as idioms, literary quotations, set expressions in journalism writing and formal business style of speech is defined: to express the emotional and mental state of the writer.