Abstract: The subject of the research is the concept of poetic language developed by an Italian poet and philologist Giacomo Leopardi. Analysis involves his Leopardi's philosophical works about the language and historical development of the mankind as well as his poetic works on ancient plots, first of all, his 'Operetti Morali' and 'Zibaldone'. Leopardi's concept of poetic language is one of the least studied topics in the Italian poet's creative writing. Based on the analysis of Leopardi's works, the author of the article views the process of creation of Leopardi's concept of poetic language as a late response to The Quarrel of the Ancients and the Moderns. In her article Balaeva uses the methodology of theoretical poetics that is aimed at systems analysis of Giacomo Leopardi's concept of poetic language. The concept of poetic language is one of the central topics in theoretical and philosophical works of the Italian author. The novelty of the research is caused by the fact that this is an understudied aspect of creative work of the Italian's poet and philospher. The main conclusion of the research is the proof of the relationship between The Quarrel of the Ancients and the Moderns and late works of Giacomo Leopardi. Giacomo Leopardi's concept of the poetic language viewed in terms of The Quarrel reveals mechanisms of the union of philosophy and poetry in theoretical (Zibaldone) and literary (Operetti Morali) works of the Italian poet.