Probiotics are nonpathogenic live microorganism that can provide a diverse health benefits on the host when consumed in adequate amounts. Probiotics are consumed in diverse ways including dairy product, food supplements and functional foods with specific health claims. Recently, many reports suggest that certain probiotic strains or multi strain mixture have potent immunomodulatory activity in diverse disorders including allergic asthma, atopic dermatitis and rheumatoid arthritis. However, underlying mechanism of action is still unclear and efficacy of probiotic administration is quite different depending on the type of strains and the amounts of doses. We and others have suggested that live probiotics or their metabolites could interact with diverse immune cells (antigen presenting cells and T cells) and confer them to have immunoregulatory functions. Through this interaction, probiotics could contribute to maintaining immune homeostasis by balancing pro-inflammatory and anti-inflammatory immune responses. However, the effect of probiotics in prevention or modulation of ongoing disease is quite diverse even within a same species. Therefore, identification of functional probiotics with specific immune regulatory property is a certainly important issue. Herein, we briefly review selection methods for immunomodulatory probiotic strains and the mechanism of action of probiotics in immune modulation.