Disclosed is an immunopotentiating composition comprising an effective immunostimulating substance which can activate natural immunity and a subsequent immunity mediated by lymphocytes without causing any damage to cells. Specifically disclosed is an immunopotentiating composition which is characterized by comprising, as an active ingredient, an immunostimulating substance produced by decomposing at least one bacterium selected from an MRE symbiotic bacteria group consisting of Bacillus sp. (FERM BP-11209), Lysinibacillus fusiformis (FERM BP-11206), Bacillus sonorensis, Lysinibacillus sp. (FERM BP-11207) and Comamonas sp. (FERM BP-11208).