Premature birth is a global clinical problem. Early colonization and development of the neonatal gut microbiome is critically important with a profound impact on the host lifelong health. We will sequence V3-V4 region of 16S rRNA amplicons of 581 stool DNA from a cohort of 51 PT infants and 50 FT infants to examine the microbial profiles. A random-effects generalized least square regression model was used to compare the difference in the main bacterial groups over time with the adjustment for multiple variables including gestational age and use of antibiotics .