Abstract: By growing Bacillus natto and lactic acid bacteria on steamed soybeans in the presence of triturated mushroom and carbon sources for the cultivation of lactic acid bateria, there is obtained a fermentation food of soybeans grown with both live bacteria. As compared with soybeans grown with Bacillus natto alone ("Natto"), the present fermentation food lacks objectionable off-flavor or an ammonia odor and keeps its quality unchanged for a longer period.