Abstract Probiotic microorganisms have generated a great interest in the scientific community to understand the complex mechanisms underlying their beneficial effects. Probiotic commensal organisms are recognized to be modulators of innate and adaptive immune responses. They work by activation of immune response and yet are able to suppress the over-inflammatory responses.The signalling mechanisms usually involve the innate pattern recognition receptors such as Toll-like receptors which recognize the microbe-associated molecular patterns leading to activation of immune signalling. Moreover, probiotic microorganisms also modulate the intestinal barrier function by inducing defensin production and regulating the immune signalling. Increasing evidence also suggests that induction of epithelial signalling by intestinal microbiota can modulate barrier functions, defensin production and regulate inflammatory signalling. Probiotics also act by activating the cell mediators of innate immunity such as dendritic cells, T effector cells and macrophages. The present review focuses on the immunomodulatory role of probiotics.