Objective：To investigate the effects of marrow-derived MSCs on the lung damage in new born rats suffering from hyperoxia. Methods：Marrow-derived MSCs were separated, cultured, amplificated and labeled with BrdU. Thirty-two three-day-old SD rats were randomly divided into four groups（A,B,C,and D）. Rats in group B and group A were exposed to 95% oxygen for 7 days, then they were injected with MSCs of 5 × 104 and PBS into tail vein respectively. Rats in group C and group D lived in normal air and were injected with MSCs of 5 × 104 and PBS into tail vein respectively at the same time. Immunohistochemistry（IHC） staining was used to determine the expression of 5-bromo-2-deoxyuridine（BrdU） and vascular endothelial cell growth factor（VEGF） 72 h later. Radical alveolar counts（RAC） of the lungs in the rats were counted under light microscope. Results:The labeled MSCs were detected in the lungs of rats treated with MSCs, but no BrdU-positive cells were found in two untreated groups（A and D）. There were significant differences in the levels of VEGF and RAC among four groups（P < 0.05, P < 0.01 respectively）. Conclusion:BrdU-labeled marrow-derived MSCs can be implanted into lungs of new born rats suffering from hyperoxia. The protective effect of MSCS on the damaged lungs induced by hyperoxiab might be related to the increased expression of VEGF.