Objective: To study the dynamic changes of intestinal flora in infants of Mongolian and Han nationality

and the effects of antibiotics on intestinal flora. Methods: Breast-Fed infants born in Inner Mongolia People’s Hospital from Jan. 2016 to Jun. 2018 were collected. All children were divided into the healthy infants of Mongolian and Han nationality and infants who had been treated with antibiotics for 2 to 28 d after birth. Stool cultures were performed within 3 h

7 d and 42 d after birth. The quantity of Lactobacillus and Bifidobacterium was detected by polymerase chain reaction (PCR). Results: With the increase of age

Lactobacillus and Bifidobacterium increased in infants of Mongolian and Han nationality (P<0.05). On the 7th and 42nd d after birth

the growth rates of two kinds of bacteria in infants of Mongolian were significantly higher than that in infants of Han nationality (P<0.05). In infants of Mongolian and Han nationality of the same age

the number of Lactobacillus did not change significantly after the use of antibiotics (P>0.05)

while Bifidobacterium decreased significantly after the use of antibiotics (P<0.05). Conclusion: The number of Lactobacillus and Bifidobacterium is higher in the intestine of infants of Mongolian

while the number of Bifidobacterium is in a decreasing tendency when antibiotics are use