The article deals features of studying syntactic connections, on the basis of which we determine the formal-syntactic structure of sentence units. The main problem of studying syntactic connections is clarified: 1) the difference between syntactic connections and semantic-syntactic relations; 2) differential features of syntactic connections; 3) predicative connection as the main type of syntactic connection; 4) signs of subordination connection in simple and complex sentences; 5) connection of word, determinant and indirect connections as types of subordination connection in a simple sentence; 6) signs of compound connection; 7) features of undifferentiated and double syntactic connections. To determine the components of a sentence, it is important to distinguish between syntactic connections and semantic-syntactic relations. The syntactic specificity of the relations between the members of the sentence on the basis of the separation of their differential features is characterized. The direction of formal-syntactic dependence (interdependence, unidirectional dependence and absence of dependence) is the main differential feature of delimitation of basic syntactic connections. Peculiarities of predicative connection formation are traced; the subordination connection is analyzed and its varieties are systematized: word’s connections, determinant and indirect connections; the specifics of compound connection is established; undifferentiated syntactic connection is characterized; the double syntactic connection is analyzed. Syntactic connections are important for determining the components of a sentence and understanding their grammatical expression.