The present invention relates to a composition for immunostirnulation usefulforpromoting IgA and secretory component productions in mucosal tissues,comprising, alone orin combination, a cell of bifidobacterium belonging to Bifidobacterium bifidumor a processedproduct thereof, wherein the bifidobacterium has an activity to stimulatesecretory cornponentproduction and a high activity to stimulate IgA production, for example, it isa Bilidobacteriumbifidum OLB 6377 strain or Bifidobacterium bifidum OLB 6378 strain.