The agrammatisms in the prose of Guillaume Apollinaire and Ossip Mandelstam are examined in this article. As a key work which is analysed the parable-tale of Apollinaire «Cemetry» (1907, 1909) is chosen. It was firstly published in the form of a poem in 1907, and only in 1909 - as a prose, but preserving totally the syntax of the poem. The prosaic and the poetic forms of this text are compared. Some poems and some texts in prose of Mandelsam are analysed as well. The devices that the poet utilizes in his poems are compared with the same devices in his prose. The conclusion is made that the language of the poetry becomes the language of the prose in the works of Mandelstam as well, as in the works of Apollinaire. The agrammatisms in the prose of both of the poets are connected with this phenomenon.