Objective: To study the association between the growth and development of extremely preterm infants at the neonatal intensive care unit (NICU) and their intestinal microfloraMethods: Extremely low gestational age infants admitted to the NICU were included in this study. The subjects were divided into the extrauterine growth retardation (EUGR) group and normal growth group, and the growth and development were evaluated at 2 and 4 weeks after birth. Meanwhile, the stool samples were taken to perform high throughput 16S rRNA sequencing of the intestinal microflora.Results: A total of 22 infants were included. There was no significant difference in the alpha diversity indexes the two groups at 2 weeks or 4 weeks after birth. The beta diversity analysis showed that the principal components of the intestinal microflora were similar between the two groups. LEfSe analysis showed that after 2 weeks of birth, the items with an absolute LDA higher than 4 included Streptococcaceae, Streptococcus, Bacteroidetes, Bacteroidales and Stenotrophomonas in the EUGR group and Enterococcaceae and Enterococcus in the control group. At the 4th week after birth, the items with an absolute LDA higher than 3 in the EUGR group included Clostriaceae, Eubacteriaceae and Eubacterium. The microbial community composition comparison showed significant differences in the principle components of Enterococcus and Streptococcus on the family and genus levels.Conclusion: The diversity and richness of the intestinal microflora in preterm infants at the NICU are significantly insufficient, and the establishment of intestinal homeostasis is obviously delayed, which may cause growth retardation.