There are growing numbers of evidence indicating the beneficial effects of normal enteric flora (probiotics) with regard to the host defense against infection. In vitro and in vivo studies have shown that probiotics such as lactobacilli and bifidobacteria have inhibitory effects on other pathogenic bacteria.This evidence, along with the results of recent clinical studies, has demonstrated the beneficial effects of probiotics in the prevention of NEC in VLBW infants.However, most of the studies reported nosocomial infection as a secondary outcome and the findings were controversial regarding probiotics efficacy in preventing nosocomial infections. There is only one study that was aimed to investigate effects of probiotic on the incidence of nosocomial infection.