Abstract: 【Abstract】 Objective To analyze the species dependent effect of bifidobacteria to the heath of the middle and elderly. Methods Total 148 healthy volunteers living in Chengdu with 5074 years old were recruited in 2015. The blood samples were collected from them and analyzed physiologically and immunologically. The fecal bifidobacterial were also analyzed by realtime fluorescence quantitative PCR (qPCR) using 16S rRNA targeting designed gene and species specific primers. Results Bifidobacterium can be detected in feces of the elderly, the detection rate was 100%, 108/g fecal. Especially, more species predominated in the infants were found the tested subjects. Bifidobacterium was positively associated with urea nitrogen ( r=0.214, P B. adolescentis was negatively associated with body mass index (BMI) ( r=－0.311, PB.catenulatum was positive to BMI ( r=0.167, PB.breve and high density lipoproteincholesterol (HDLC) were negatively correlated ( r=－0.247, P Bifidobacterium infantis and HDLC were positively correlated ( r=0.350, PB.bifidum was found to be positive associated with IgA ( r=0.365, PBifidobacterium might affect the host physiologically and immunology in the species dependent manner. Keeping intestinal bifidobacteria in the ideal species composition might be one of effective ways to slow immune senescence, and promote the health of the elderly.