Probiotic bacteria are normal inhabitants of microflora and may confer several benefits, including prevention against intestinal inflammation. However, the exact mode of action of probiotics is still largely unknown. The first line of defense against the entry of pathogens is represented by the gut membrane barrier and probiotics may prevent pathogen-induced membrane damage by inhibiting pathogen adhesion and maintaining the correct organization of the tight junction and cytoskeleton proteins. The gut immune system should not only protect the mucosa against pathogens, but also avoid hypersensitivity reactions to food proteins and normal microflora. Failure of induction or maintenance of oral tolerance has been postulated to be a cause of food allergy. Feeding probiotic bacteria may prevent or ameliorate the onset of allergic disease and the associated inflammatory reactions through mechanisms involving modulation of T regulatory cells. Breakdown in tolerance toward intestinal bacteria is a primary cause of inflammatory bowel disease. Recent studies have shown that probiotics may ameliorate experimental colitis in mice by inducing interleukin 10 and interleukin 10-dependent T regulatory cells. In this article, an update of the anti-inflammatory activity of different probiotics and of the more accredited mechanisms underlying such activities are reported.