Objective To establish the theoretical basis of the probiotic application among very low birth weight(VLBW) infants,the efficacy of probiotics on the gut microbiota of VLBW infants on the 14th postnatal day was studied.Method The VLBW infants admitted to BaoAn Maternal and Child Care Hospital from January 2015 to December 2015 were randomly assigned into probiotics group and placebo group.From the first feeding to corrected gestational age of 36 weeks,probiotics group was treated with a combination of Bifidobacterium and Lactobacillus while placebo group with placebo.Fecal samples were collected on the 1st and 14th postnatal day.Total bacterial DNA was extracted and sequenced using high-throughput 16S rRNA gene sequencing on MiSeq sequencing platform.Result A total of 21 VLBW infants were enrolled,9 in probiotics group and other 12 placebo group.No significant differences of clinical data existed between the two group (P ＞ 0.05),The abundance and diversity of microflora (P ＞ 0.05) on the first day between the two group were similar.Compared with placebo group,the relative abundance of Bifidobacterium and Lactobacillales in stool samples on the 14th day was significantly increased,while the Halomonas was significantly decreased.The relative abundance of the Shannon-index was increased,but without significant difference (P =0.16).Conclusion Enteral supplementation of probiotics in VLBW infants may increase probiotic bacterium and microflora diversity.