Introduction. The results of numerous studies indicating the relationship between the development of reactive arthritis (ReA) and the disturbance of the intestinal microbiocenosis give rise to interest in commensal microorganisms that make up the intestinal microbiota as potential initiators of immune-dependent inflammatory diseases of the joints. In this regard, the question of the expediency of using probiotic preparations for the correction of ReA patients intestinal microflora is of practical interest.The purpose of the study was to evaluate the effectiveness of Lactobacillus rhamnosus LGG (LGG) in the preventive treatment of children with ReA to prevent the development of relapses.Materials and methods. Clinical and microbiological study included 60 patients with ReA from 3 to 17 years old, who were divided into two groups, 30 children each. Patients of the group 1 received courses of treatment with LGG in the inactive phase of the disease. Patients of the group 2 (comparison group) were not treated with probiotic. The criteria for the effectiveness of treatment were the number of relapses of ReA during follow-up observation for 1 year; dynamics of intestinal microbiocenosis condition according to the following parameters: indicator of microbial contamination (IMC) of intestinal microsymbionts; ability to biofilm formation (BF); levels of lactoferrin and lysozyme in coprofiltrates.Results. In patients treated with LGG, relapses of arthritis were significantly less frequent during 12 months of prospective observation relative to the comparison group. Patients of the group 1 showed positive dynamics of the state of intestinal microbiocenosis: a decrease in the severity of dysbiosis, a decrease of lactoferrin and lysozyme level in coprofiltrates, IMC and BF of opportunistic microorganisms against the increase IMC and BF in bifidobacteria and lactobacilli.Conclusions. The use of LGG in the treatment of children with ReA in the inactive phase of the disease contributes to the correction of intestinal microbiocenosis disorders and reduces the number of arthritis relapses.