Probiotics are becoming more and more common means of combating intestinal diseases of various origins: infectious pathologies, chronic inflammation, autoimmune disorders. The complex action, coupled with low side effects, makes probiotics promising drugs, especially in veterinary medicine, with an increasing trend towards the inefficient use of antibiotics in the livestock industry. One of the main mechanisms of probiotics action - modulation of host immunity - is perhaps the most difficult and, at the same time, the most actively studied since it is crucial for therapy. Immunobiotics (probiotics that modulate the host's immune response) interact with various innate and adaptive immune cells, changing the expression of pro- and anti-inflammatory cytokines. This action is provided by both the cellular components of probiotic microorganisms and their metabolites and is primarily associated with the host's immunocompetent cells' pattern-recognition receptors, although other molecular mechanisms also exist. This review aims to briefly describe both the molecular mechanisms of immunomodulation by probiotics and the prospects for their use in veterinary medicine. © The Authors, published by EDP Sciences, 2020.