The syntax of the texts of Belarusian and Slovak folk fairy tales is viewed as an aesthetically significant communicative way of grouping the language units in the functioning of the language. The ratio of the simple and complex sentences is an essential attribute of the language of prose folklore that has the similar tendency of prevalence of the complex sentences in both Belarussian and Slovak material. The common attribute is the presence of a certain amount of the texts with significant preponderance of the simple sentences. The Slovak material shows higher percentage of the compound sentences. Thus the volume of a text is not essential. The dialogical form of the speech without the words of the author acts as a differential attribute of a large amount of the simple sentences. The inclusion of the complex sentences into the structure of a fairy-tale formula, repeated paraemia or loci communes is an additional condition of the increase in their quantity. The quantity of the predicative parts in the structure of a complex sentence varies from 2 to 15 (the Slovak language) or 8 (the Belarussian language). In both languages the complex sentence with two predicative parts prevails in the analyzed texts. In the Slovak texts compound sentences with three predicative parts are used more often. The Belarus material reflects a vivid dynamics in the structurization of semantically repeated or transformed text fragments by means of the different kinds of the simple and complex sentences as the factor of variability of the linguistic means which is essential in the system of the Belarussian literary language.