The plant-derived Pediococcus pentosaceus NB-17 was isolated from Japanese traditional vegetable pickles. The production of cytokines from mouse spleen cells co-cultivated with heat-killed bacteria was investigated in vitro. The bacteria significantly induced secretion levels of interferon (IFN)-gamma and interleukin (IL)-12 p70, and suppressed IL-4 productions in ovalbumin (OVA) sensitized mouse spleen cells. Therefore, the bacteria could effectively stimulate immune activities and showed allergic inhibitory effects. Further study on acid tolerance was performed under simulated gastric conditions and NB-17 showed resistance to simulated gastric acidity at pH 3.0 and pH 2.5. Moreover, after oral administration of the intact cells to rats, bacterial colonies derived from feces were analyzed by random amplification polymorphic DNA (RAPD). It was confirmed that the administered strain NB-17 remained alive in feces. These results suggest the possibility to use the P. pentosaceus NB-17 as functional foods.