Probiotics are defined as "Live microorganisms" which when administered in sufficient amounts confer a health benefit to the host. They are consumed as microbial food supplements. The mechanism of action of probiotics is associated with their ability to enhance immune response, compete with pathogenic microbes for adhesion sites, to antagonize these pathogens and production of antimicrobial substances. Immunomodulatory effect of probiotics can be explained by molecular and proteomic studies. Health benefits of probiotics includes prevention and treatment of various health conditions and diseases such as gastrointestinal disorders, lactose intolerance, irritable bowel syndrome, inflammatory bowel disease, Necrotising colitis, allergies, urogenital infections, various cancers, Arthritis, AIDS, Upper respiratory infections, oral health such as prevention of dental caries, periodontal diseases and haliotis as well as many other effects which are under exploration. The result of several clinical investigations proposes that probiotics may exert beneficial effect in preventing and treating various diseases to manage human health. Though, many of this clinical research needed validation to provide results for clinical regime. This review illustrates the health benefits of probiotics in various diseases and their possible mechanism and also highlights current challenges for future studies.