The article presents results of studies on specification of the size of nucleic acids of Ps.s-7 UlGAU and Ps.s-27 UlGAU bacteriophages. The relevance of the research on classification of bacteriophages by type and size of nucleic acid is substantiated in the introduction of the article. It was established, by the method of extraction on magnetic particles and phenol-chloroform extraction, that the maximum calculated size for the DNA of Ps.s-7 UlGAU bacteriophage (isolated from a soil sample,

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... racteristics: lytic activity, determined by the Gracio method, - 2.0 ± 0.1x109 pfu / ml, by Appelman's method - 10-8, drip test - n9; spectrum of lytic action - 85.7%) was 38137 bp, for Ps.s-27 UlGAU bacteriophage (isolated from a soil sample, characteristics: 1.0 ± 0.1x109 pfu / ml according to Grazio, according to Appelman - 10-8 , drop test - n9; spectrum of lytic action was 85.7%) DNA size was 23744 bp. The studies used a DNA molecular weight marker Quick-Load Extend DNA 500-48500 bp, a Nanodrop 2000 / 2000c spectrophotometer (ThermoFisher), and a PAGE electrophoresis technique. The obtained data will make it possible to specify the phylogenetic relationship of Ps.s-7 UlGAU and Ps.s-27 UlGAU bacteriophages with bacteriophages annotated in the NCBI database, using Protein BLAST, active against phytopathogenic Pseudomonas syringae bacteria, causing tumor neoplasms, rotting, growth cessation and death of a part of plants cultivated by humans without decay, chlorosis, necrosis, etc.