Various types of semantic-syntactic relations can be observed in the structure of compound sentences. Typically, in the presence of specialized formal-semantic means of explication, the process of their identification by the addressee occurs quickly and smoothly. However, if conjunctions are absent or have atypical manifestations, the semantic-syntactic relations between the predicative parts of a compound sentence are hidden. This complicates their establishment by the recipient, and therefore prevents him/her from adequately perceiving and understanding the communicated information. Consequently, systematic research of the specifics of hidden semantic-syntactic relations in different types of compound sentences is required. The purpose of this article is to conduct a comprehensive analysis of hidden semantic-syntactic relations at the level of compound sentences in the modern Ukrainian language in linguistic and linguo-didactic aspects. The achievement of the goal was facilitated by the application of linguistic methods such as descriptive, structural, transformational, componential analysis, and contextual-semantic analysis. The research is based on the material of sentence constructions selected from the texts of the artistic style of the modern Ukrainian language. Results. In the system of compound sentences, hidden semantic-syntactic relations primarily represent causal and conditional sentences with an semantic conjunction «і», which is a purely formal marker of coordinate connection. Hidden semantic-syntactic relations are also characteristic of compound adjoining constructions with conjunctions «і», «а», «але». Their establishment by the recipient is facilitated by the lexical content, the arrangement of the predicative parts, syntactic parallelism, the correlation of the forms of predicate verbs, and the intonation of the utterance. Observations of compound sentences in fictional texts indicate that the conjunction «і» is not always a marker of actually coordinative relations, «а» – of comparative, and «але» – of adversative relations. Although each of them undoubtedly specializes in expressing its own relation, through appropriate transposition into secondary semantic spheres, partially losing their semantic significance, they become indicators of adjoining semantic-syntactic relations, which acquire a hidden character in the structure of a compound sentence. Originality. The hidden content relations in various structural-semantic types of compound sentences are characterized. The derivational and synonymous relations between compound and complex subordinate constructions are established. Criteria for identifying hidden semantic-syntactic relations at the level of compound sentences are offered. This will contribute to the proper decoding of the information contained in it by the addressee and the implementation of high-quality syntactic analysis in Ukrainian language classes in educational institutions. Conclusion. Hidden semantic-syntactic relations in compound sentences can hinder effective verbal communication between the addresser and the addressee. This requires the participants of the communicative process to have thorough linguistic knowledge of structural-semantic specificity, syntactic synonymy, derivational connections, intonation, punctuation, stylistic use, and expressive possibilities of compound sentences. Sufficient linguistic-communicative competencies will enable the recipient to establish these relations and adequately perceive the communicated content, while education seekers will be able to properly analyze expressions at the syntactic level. Research on hidden content relations in complex subordinate and conjunctionless constructions is considered promising.