It is devoted to the problem of phraseology in syntax, not studied enough yet. The notion of phraseology in linguistics is perceived first of all as connected with lexical structure of language. But in syntax constructions this phenomenon is presented widely and figuratively. One type of syntax phraseological units are the sentences of phraseological structure (PS). Their basic essential grammatical peculiarities are considered. PS are build up according to phraseological model, which includes: constant, fixed components, that means reserved words in their secondary use, defining their composition and phraseological meaning and free, variable component, which is lexically free, due to this there can be build many utterances on one model. Compare: Тоже мне город; Тоже мне праздник; Тоже мне помощник (That’s not a city; That’s not festival; That’s not an assistant). Thus, PS have dual nature, combine features of phraseological units and features of sentence. Basic part is devoted to variation of PS. This aspect of analysis is not chosen accidentally: variation is a characteristic feature of PS and that is what they are different from lexical phraselogical units. The variation of building is not a characteristic feature for them. The aim is to analyze the reason of PS variation and to reveal the ways of its appearance. It is shown, that variation is the confirmation and appearance of their grammatical essence, their dual nature. Some variants of PS reflect their phraseological nature, others are conditioned by their syntactic features. The variants of first type are conditioned on the word of constant type is replaced by another, both lexically and grammatically wasted (Какой / Какое / Где / Куда там прочитал! (But that won’t do to read!)). The variants of the second type are conditioned on by sentence features of FS, but grammatical features of free component define the form of constant, compare: Какой это певец, Какой он певец, Какая это певица, Какая она певица: (What a singer, She / He is not a singer) but only: Какой это праздник (What a festival). Variations of FS do not conflict with phraseological nature of FS as it is realized within strict frames of their stability and repeatability.