The main goal of our research is to collect, systematize and analyze the proper names of all seas that are in the Ukrainian language. The purpose of the research involves solving the following tasks: 1) to draw up a register of pelagonyms; 2) determine their denotative and characteristic features; 3) find out etymological and word-forming features; 4) describe the peculiarities of functioning in the Ukrainian language; 5) establish the defining features of this type of proper names. The object of analysis is 238 pelagonyms, and their denotative-characteristic, etymological-word-forming and functional features are the subject of analysis. In the process of analysis, we used genetic (to determine the origin of proper names), etymological (to find out the features of names creation), descriptive (to determine the extralingual features of pelagonyms), structural (to characterize the structure of names), functional (to describe features related to the functioning of seas names in texts of various styles) research methods and the method of quantitative calculations (to determine the productivity of different types of pelagonyms). It was established that compound constructions (the most productive models are "noun + adjective" and "noun + noun"), formed by a syntactic method, with combined motivation (in particular, locative-, memorial-, and qualitative-substantial) dominate, they are derived from onyms and appellatives. Geographical terms and anthroponyms or toponyms prevail in their composition. Most pelagonyms are ancient, hybrid, lowfrequency, emotionally neutral names that have a known and obscure etymology, are used in a scientific style, are elements of language (not speech), belong to the passive vocabulary, are unknown to the general public, and are devoid of ethnocultural meaning. In the future, we plan to pay attention to the general characteristics of other proper names: both open water bodies (for example, loughs or streams), and such categories as oikonyms, oronyms, or choronyms. Over time, this will make it possible to form a complete picture of the Ukrainian toponymy.