Background. Functional disorders of the gastrointestinal tract represent one of the most urgent problems among children in the first year of life. Aim: to determine the peculiarities of microbiocenosis of large intestine in children with varying degrees of dysbiotic conditions of the gastrointestinal tract. Materials and methods. Material for the study included 354 coprological samples isolated from children with functional disorders of the gastrointestinal tract. Depending on the degree of dysbiotic disorders of the colon, the children were divided into comparison groups: group 1 - children with grade 1 dysbiosis (n = 15), group 2 - 45 children with grade 2 dysbiosis, group 3 consisted of 149 children with grade 3, and group 4 consisted of 145 children with grade 3 of dysbiotic disturbances and K. оxytoca vegetation. Identification was performed by standard methods. Results. All four groups were characterized with changes in the qualitative composition of the indigenous biota with predominance of E. coli with atypical properties (haemolytic (up to 26,7 %) and labourmigration activity (to 33,3 %)). Groups with grade 3 dysbiosis were characterized by the presence of aggressive symbiotes in diagnostically significant concentration of S. aureus, Clostridium spp., Candida spp., Enterobacter spp., Proteusspp., P. aeruginosa. Conclusion. The emergence of Klebsiella oxytoca in the colon of children is an evidence of the violation of compensatory-adaptive reactions of the organism, which in turn is characterized by a decrease and a change in the qualitative composition of the indigenous biota by connecting the more aggressive representatives of the bacterial agents.