Background. Gestational diabetes is a condition that arises due to impaired metabolic processes against the background of insulin resistance and an increase in blood glucose levels during pregnancy. This pathology leads to a significant number of pregnancy and childbirth complications, high child perinatal morbidity and mortality, and its prevalence varies throughout the world. The aim of the work was to determine the taxonomic composition, population level and microecological indicators of the macroorganism-microbiome ecosystem of the symbiotic colon microbiota in women with gestational diabetes. Materials and methods. The microbiological examination of the colon contents was carried out in 26 pregnant women aged 18 to 35 years. The clinical material for microbiological examination was the fresh colon contents (faeces) taken from medium portions, which were collected in sterile (after autoclaving) vials. Results. According to the results of the work, it was found that during gestational diabetes, the taxonomic composition and microecological parameters of the macroorganism-microbiome ecosystem of the colon microbiota in women are impaired due to the biotope contamination with pathogenic microorganisms (E.coli HLy+) and opportunistic pathogens (E.coli Lac-, P.mirabilis, P.vulgaris, E.cloacae, C.diversus, S.marcescens), enterobacteria, C.albicans, P.niger and bacteria of the genus Clostridium. Alterations in the taxonomic composition and microecological indicators of the colon microbiome in women with gestational diabetes lead to multidirectional changes depending on the taxon: a decrease in the population level of bacteria, which are the most important in terms of representation in the human colon microbiome, with a multifunctional role in maintaining microecological homeostasis (bacteria of the genus Bifidobacterium — by 17.59 %, Lactobacillus — by 38.37 %) and an increase or a stable trend towards an increase in the population level of opportunistic enterobacteria P.mirabilis by 26.67 %; among other enterobacteria, the population reaches high levels (from 6.390 ± 0.009 lg CFU/g to 7.46 ± 0.17 lg CFU/g), the level of Staphylococcus in increased by 35.94 %, C.albicans — by 26.74 %, P.melaninogenicus — by 55.93 %.