It is intended to provide a lactic acid bacterium selected from the groupconsisting of Lactobacillus ONRIC b0239 (FERM BP-10064) and LactobacillusONRIC b0240 (FERM BP-10065); and a composition (in particular, a compositionin the form of a food, a drink or a drug) containing the lactic acid bacteriumand having a mucosal immunopotentiation effect. The above-described lacticacid bacterium and the composition containing the same can exert an excellentmucosal immunopotentiation effect and, therefore, are useful in strengtheningthe biological defense system.