The article deals with the study of the Ukrainian-Bulgarian interdialectal and interlingual influence in the multiethnic and multilingual area in the south of Ukraine, in the interfluve of Dniester and Danube. Polylingualism, dialectal diversity, the state and functioning of the South Bessarabian Ukrainian and Bulgarian dialects have been actively studied since the mid-twentieth century, but no comparative studies and comprehensive analysis of the linguistic situation and modern interference have been conducted, so work in this area is relevant and necessary. The dialects of different languages of the studied area have been unevenly studied descriptively and linguogeographically. Descriptive studies describe the structure of individual dialect systems, analyze certain structural levels, mainly in comparison with the literary language and within the principles of national dialectological schools, but practically ignore the territorially adjacent and mixed dialects belonging to different languages and the processes of interference. The purpose of this paper is to study two types of Ukrainian-Bulgarian mutual influence: at the interdialectal level and the influence of the Ukrainian literary language on the Bulgarian dialects of the Odesa region. The task is to systematize and generalize the phenomena of interference between two contacting languages and their dialects. The material of the study was based on authors’ own observations during field dialectological expeditions to the region, as well as material selected from the corpus of already published descriptions of individual dialect systems of South Bessarabian Ukrainian and Bulgarian dialects. It is noted that some Turkisms in Ukrainian dialects are borrowed through the mediation of Bulgarian diasystems and, moreover, constitute a corpus of regional integratisms. Two types of the latest borrowings from the Ukrainian literary language have been documented: a) officialese vocabulary which replaces previously used similar units of Russian-language origin; b) precedent statements and expressive vocabulary. It is stated that today there is no systemic Ukrainian-Bulgarian interference, but instead numerous borrowings are documented, the source of which is television and school.