Supplemental oxygen is commonly used to treat severe respiratory failure,while prolonged expo-sure to hyperoxia can induce acute lung injury characterized by the accumulation of reactive oxygen species(ROS)and pulmonary inflammation.Dysregulation of microRNAs contributes to multiple diseases,including hyperoxia-induced acute lung injury(HALI).In this study,we explored the roles of miR-20b in mediating the response of type II alveolar epithelial cells(ACE lls)to hyper-oxia and the potential underlying mechanisms.We found that miR-20b was significantly decreased in the lung tissues of HALI models and H202-treated ACE lls.Hyperoxia induced the release of TNF-a,decreased the mitochondrial membrane potential,and led to excessive ROS production and cell apoptosis.Overexpression of miR-20b suppressed the hyperoxia-induced biological effects in ACE lls.miR-20b negatively regulated the expression levels of Mitofusin 1(MFN1)and MFN2,the two key proteins of mitochondrial fusion,via complementarily binding to the 3'-untranslated regions of mRNAs.Furthermore,both in vivo and in vitro,upregulation of MFN1 and MFN2 aggravated lung damage and cell apoptosis that were alleviated by miR-20b overexpression.These results provided new insights into the involvement of the miR-20b/MFN1/2 signaling pathway in HALI.