Probiotic is live non-pathogenic microorganisms which confers beneficial effects on host. It is available in the form of dairy products, cheese, butter, yogurt and fermented products for maintaining microbial flora. Probiotic act through different mechanisms -inhibition of proliferation of pathogenic bacteria, production of antimicrobial substances, enhance immune system by modulating different immune mechanism and by regulating intestinal permeability by strengthening pathogenic barrier. Probiotic is effective in different clinical conditions like diarrhea, intestinal inflammatory disorders, bacterial infection, allergic conditions, immunomodulation, viral infection and in oral health. Probiotic shows antioxidant activity by releasing different antioxidant enzymes which neutralize reactive oxygen species to avoid cellular damage and decrease the risk of chronic disease conditions. Probiotic shows antimicrobial property against pathogen by maintaining intestinal pathogenic barrier and production of antimicrobial peptides, H2O2, bacteriocins, organic acids by gut epithelial cells. Lactobacillus as probiotics are being used for long time due to their safety and efficacy, but other probiotics show minor side effects like thirst, constipation, nausea, vomiting, abdominal pains. Probiotics rarely show harmful effects. KEYWORDS- Probiotics, antidiarrheal, antimicrobial, antioxidants