Abstract: The present invention relates to bidifobacteria strains having tolerance in the gastrointestinal environments and to a method for culturing the same. The strains of the invention are Bifidobacterium longum (ATCC 55815, 55816, 55817, 55818) which have tolerances against bile salt, acid and oxygen and which have been obtained through mutagenesis and screening for tolerances against bile salt, acid and oxygen by using acid-tolerant Bifidobacterium longum Y1 and Y2 strains (ATCC 55813 and 55814) isolated from healthy infant feces as the parent strains. The strains of the present invention show excellent growth under aerobic condition in the presence of skim milk without supplement of other growth promoting substances. This oxygen-tolerant property is favor for their industrial production.