The gut microbiota is a community of microorganisms that live in the digestive tract of living beings and form bidirectional symbiotic relationships with them. It is known that gut bacteria play an important role in maintaining the functioning of the host organism, and disruption in the normal composition of the gut microbiota can contribute to the development of many diseases. The study of microbiota has been gaining popularity in recent years, and its influence on the course of various pathological conditions is becoming more and more undeniable. Due to the growing evidence supporting the connection between the gastrointestinal tract, microbiota and brain, the term «microbiota—gut—brain axis» has appeared. It regulates the functions of the central nervous system, affecting the mood, behavior of the host and, therefore, is involved in the pathogenesis of various mental disorders. Bipolar disorder, a long–known affective mental illness of an endogenous origin, is no exception. The review analyzes the evidence on the relationship between gut microbiota and bipolar disorder, as well as an overview of additional treatments for this disease that affect the microflora of the human body.