17It is intended to provide Bifidobacterium longum having the following bacteriological properties and microbial powders, foods and beverages containing this Bifidobacterium longum: (1) having such fermentation ability as to make a milk base medium to pH 4.6 or below; (2) showing a survival rate of 50% or more in the case of, after attaining pH 4.4 to 4.6 in a milk base medium, quenching and storing at 10.degree. C. for two weeks; and (3) having such gastric juice tolerance as to yield a survival rate of 10% or more in the case of storing in artificial gastric juice (pH 3.0) at 37.degree. C. for two hours.