The article analyzes the scientific material of Ivan Erofeiv's researches on the tradition of Ukrainian Dumas, characterizes the methodology, peculiarities of work with the source base, with variant material, classification by main motifs, etc. The focus is on the second most important folkloristic research of the scientist “Crimea in the Little Russian folk poetry of the XVI-XVII centuries, mainly in Dumas”, dedicated to the memory of Professor Volodymyr Antonovych. The research activity of the folklorist is analyzed in the context of the scientific research of the Kiev scientific school at the beginning of the 20th century. In the first decade of the 20th century, Ukrainian folkloristics suffered significant losses - such brilliant scholars of the Kyiv school as M. Dashkevich, V. Antonovych, P. Zhitetskyi passed away. As a result of the socio-historical cataclysms of the beginning of the century, some scientists tragically died, and others emigrated. However, scientific research in the field of folkloristics is continued by talented students of the Kyiv School, among whom the figure of researcher Ivan Yerofeiv, who distinguished himself, in particular, as a researcher of such an original and rather complex genre of Ukrainian folk poetry as Dumas, occupies a prominent place. The basis for the scientific research "Crimea in the Little Russian folk poetry of the XVI-XVII centuries, mainly in Dumas" was the previous work of the researcher "Ukrainian Dumas and their versions". In the new work, a range of problems related to the reflection in the oral poetic tradition of one of the most tragic and heroic periods in the history of Ukraine is the era of the national liberation struggle of the people, its struggle for statehood against numerous external enemies was raised. The question of the relationship between Ukrainians and their formidable Muslim neighbor will be interpreted here through the prism of folk poetic perception and with the involvement of a wide array of historiographical material. The essay highlights mainly the most characteristic motifs of Ukrainian dumas and historical songs, which reflected the relationship between two hostile forces which are the Cossacks and the Muslim world. However, this work cannot be considered superficial, since a large amount of sporadically conceived folklore material was involved in the analysis namely numerous versions of works, domestic and Polish historiographical sources. I. Erofeiv builds his research exclusively on the analysis of dumas and historical songs of more ancient origin, where generalizing pictures of that time reality are reproduced in typical images, without connection with specific persons or events. Simultaneously, a group of songs depicting the victories of the Cossack army over the Turks and Tatars during the national liberation war under the leadership of Bohdan Khmelnytskyi falls out of sight. The study of the songs of this group would provide interesting material for elucidating folklore concepts regarding the attitude of the Ukrainian people to Khmelnytskyi's foreign policy aimed at alliance with Muslim states.