We screened lactic acid bacteria which had cellular or humoral immunomodulatory function from 51 strains isolated from Mongolian fermented milk by measuring the inductive activity of IL-12 and INF-γ or IgM, IgG and IgA, respectively. Two strains induced large quantities of IL-12 and INF-γ and had cellular immunomodulatory function, and 3 strains induced large quantities of IgA and had humoral immunomodulatory function. The probiotic properties of these 5 strains were studied by measuring the tolerance to stomach acid, bile and pancreatic fluid and the adherence to human enterocyte-like Caco-2 cells in in vitro tests. Results showed that the N-17 strain (Lactobacillus plantarum), which induced large quantities of IgA, strongly tolerated stomach acid, bile and pancreatic fluid and expressed strong adherence to human enterocyte-like Caco-2 cells. In addition, survival of the N-17 strain during passage through the gastrointestinal tract of mice was examined after 6, 12, 24, 36, 48, 60 and 72 hr of oral administration to mice. Six hr after oral administration, the highest number of viable cells of the strain appeared from feces, and almost all of the administered bacteria were recovered within 48hr. These results suggested that the N-17 strain isolated from Mongolian fermented milk induced large quantities of IgA and showed high survival during passage through the mouse digestive tract. Therefore, this is an excellent probiotic strain which has humoral immunomodulatory function and may be useful as a carrier for the oral vaccine.