Intestinal bacterial proliferation is an important aspect of gastrointestinal injury in neonatal necrotizing enterocolitis (NEC). In the present investigation, we examined the protective action of oral supplementation with Saccharomyces boulardii (S. boulardii), non-pathogen probiotic yeast, against hypoxia-reoxygenation (H/R)-induced NEC in young mice. Young mice were divided into three groups; Group 1 mice (untreated) were subjected only to hypoxia-reoxygenation; Group 2 mice were subjected to hypoxia-reoxygenation and were then given Iyophilized S. boulardii (10 mg suspended in 0.5 ml saline) twice a day by orogastric intubation for 10 days. Group 3 mice served as controls. Hypoxia was induced by placing young mice in a 100% CO2 chamber for 5 min. After hypoxia, the young mice were reoxygenated for 10 min with 100% oxygen. We examined the intestinal lesions by light microscopy and measured intestinal generation of PAF and TNF-alpha in the H/R-induced model of NEC. In the probiotic group, NEC-induced intestinal tissue damage was greatly attenuated, with necrosis partially limited to the mucosa. Both intestinal tissue PAF and TNF-alpha concentrations were significantly higher in the untreated group than in controls (p < 0.001). S. boulardii-supplemented young mice showed a significant decrease in intestinal generation of PAF compared with untreated young mice (p < 0.05). On the other hand, no significant difference was observed in the intestinal concentration of TNF-alpha between untreated and probiotic groups (p > 0.05). The present study suggests that hypoxia/reoxygenation plays an important role in the pathogenesis of NEC and supports hypothesis that especially PAF and TNF-alpha are involved in the pathophysiological mechanism of H/R-induced NEC. This study also demonstrates that dietary supplementation with S. boulardii ameliorates the histologic evidence of H/R-induced intestinal injury. Based on these findings, the beneficial effects of probiotic S. boulardii in this model of NEC are mediated via mechanisms inhibiting intestinal proinflammatory mediator release.