FIELD: chemistry of heterocyclic compounds. SUBSTANCE: product: derivative of oxazolidinone of the formula (I): 
or its pharmaceutically acceptable salt where n = 1; A - piperazine ring; Y means -C1-6-alkyl, -C(O)--C1-6--alkyl, -C(O)-O--C1-6--alkyl, benzoyl, 2-benzylhydroxyethoxycarbonyl, 1,4-dioxopentyl, -N-(C1-4-алкил)2, piperidyl, morpholinyl, group of the formulas: 
; X and Z mean independently C1-6-alkyl or hydrogen being in any case indicated C1-6-alkyl can be substituted with one or some substituents taken from F, Cl, Br, CN or OR1 where R1 means hydrogen or C1-4--alkyl; U, V and W mean independently F or hydrogen; R - lower alkyl; q = 0-4. Invention proposes also method of treatment of bacterial infections in warm-blooded animals by administration of compound of the formula (I) at doses 0.1-100 mg/kg body mass/day but preferably at doses 3-50 mg/kg/day. EFFECT: improved method of synthesis. 13 cl, 1 tbl
