Abstract: The purpose of this study was to investigate the population diversity and abundance of Bifidobacterium in the intestinal tract of newborn infants to provide reference for the health evaluation and nutritional supplement design of infants. Terminal restriction fragment length polymorphism(T-RFLP)and real-time fluorescence quantitative PCR technique were used in this study to explore the population composition and relative content of Bifidobacterium in the intestinal tract of 0~6month-old(Ⅰgroup),6~12 month-old(Ⅱgroup)and 12~36 month-old(Ⅲgroup)infants in Guanzhong,Shanxi. The main results were as follows:Twenty four samples were collected,from which 5 strains were found which were Bifidobacterium longum,Bifidobacterium breve,Bifidobacterium bifidum,Bifidobacterium animals and Bifidobacterium pseudocatenulatum in three groups,besides Bifidobacterium adolescentiswere found only in Ⅲ group. The contents of Bifidobacterium in the three groups were about 10¹⁰ copies/g and the content of Bifidobacterium(10^10.44 copies/g)in groupⅠ was significantly higher than that in group Ⅱ and group Ⅲ(p<0.05). The abundance of Bifidobacterium longum and Bifidobacterium breve in the samples of Ⅰ and Ⅱ groups was higher,and the corresponding abundance in Ⅰ and Ⅱ group were 30.12%,38.02% and 33.89%,43.65% respectively.The top three abundance of species in group Ⅲ were Bifidobacterium longum,Bifidobacterium breve and Bifidobacterium bifidum,which were 23.99%,19.95% and 24.55% respectively.Taking into consideration the results we obtained,there was no significant difference in the population composition of Bifidobacterium in three groups of different age infants,and there were significant differences in abundance(p<0.05).