The human organism can be considered a complex ecosystem with a great variety of microorganisms living within it and the interactions established between microorganisms in the gastrointestinal tract and the brain are regulated by the central nervous system and enteric nervous system. Increasing evidence supports the importance of gut microbiota in regulating multiple functions related to the host's physical and psychological health. There are many factors that influence the composition of the intestinal microbiota, and physical activity is among them. It is known that physical activity has a positive effect on the human body, and in this thesis, the impact of physical activity on the microbiota-gut brain axis and mental health is explained in more detail. Many studies have pointed to the great connection and importance of the gut microflora, i.e. the intestinal nervous system and the function of the central nervous system. When the diversity of intestinal bacteria decreases, gastrointestinal and other disorders occur, including psychological disorders, and this communication pathway is known as the microbiota-gut-brain axis. Since it has been established that the gut and the brain can communicate, it is assumed that physical activity can alleviate the symptoms of various psychological disorders. Therefore, the goal of this thesis is to explain the communication path of the microbiota-gut-brain axis, how physical activity affects the microbiome and thus leads to changes in the gut and brain, and to explain the mediating role of physical activity in the influence of the microbiota-gut-brain axis on mental health.