Objective To study the effects of prolonged 85％ oxygen exposure on the expression of endothelial Sox17 in the neonatal mice lungs.Methods Thirty two C57BI/6J newborn mice were randomly exposed to air (room air group) and 85％ oxygen (hyperoxia group) within 12 hrs after birth.The mice were sacrificed at 7 and 14 days after exposure and their lungs were sampled.The lung sections were stained with hematoxylin and eosin for histological evaluation.Immunohistochemical staining was used to observe the expression of Sox17 in the lung.Sox17 mRNA and protein level was measured by reverse transcription polymerase chain reaction and Western Blot.