Gut of newborn preterm is sterile, immediately by the mother and the surrounding environment from microbial colonization. As the effects of diet, intestinal flora is rapidly changed. Preterm children significantly delay in the establishment of normal flora,during hospitalization because of no breastfeeding, use of antibiotics, enteral feeding delay, combat disease and other factors. In this study, hospitalized preterm children for the study, the prospective randomized double-blind controlled study, to find oral intestinal bifidobacteria and lactobacilli and bifidobacteria subspecies composition and distribution, and further show intestinal bacteria in premature children case group.

Preterm infants are at high risk of deeding intolerance especially low birth weight infants, Whether oral triple viable Bifidobacterium and early Micro-feeding may improve the symptoms of feeding intolerance.

84 preterm infants BW(birth weight) less than 2.5kg,entered neonatal intensive care unit(NICU) less than 24 hours and meet the Inclusion Criteria of this study will be Randomly divided into three groups, control group、 treatment group1 (Triple viable Bifidobacterium 0.5g bid po)、treatment group2 （Triple viable Bifidobacterium 0.5g bid po and early micro-feeding）. treatment period for more than 1 week. For three groups, feeding symptoms,the traits and frequency of stool of 3 days,1 weeks,2 weeks.And the stool flora measured by PCR.

Inclusion Criteria:

• preterm with birth weight <2.5kg

Exclusion Criteria:

• Gastrointestinal bleeding and NEC,Kidney,liver function abnormal and have Serious congenital malformation

The patients were randomly assigned to either a control group or a probiotic-supplemented group in the following manner. The randomization schedule was made available only to the pharmacist who supervised the quality, transport and storage of LCB. Infants were followed up until they were discharged from the hospital or died. They were withdrawn from the trial if severe adverse effects developed, or parents withdrew consent. The probiotic-supplemented group were orally administered LCB (Bifico, Shanghai Xinyi Pharmaceutical Inc. Shanghai), and the control group was fed with the same dose of luke warm water); both the preparations were supplied in identical containers. LCB was orally administered starting from day 2 after birth, at a dose of 0.5g (the numbers of Long Bifidobacterium, Lactobacillus acidophilus and Enterococcus faecalis in live>0.5*107CFU), twice per day, for 2 weeks.