Hyperoxic Acute Lung Injury (HALI) is a serious complication of prolonged high-concentration oxygen therapy, primarily leading to Acute Respiratory Distress Syndrome (ARDS), which primarily affects alveolar epithelial cells (AECs). Exosomes (Exos) derived from type II alveolar epithelial cells (AEC IIs) play a crucial role in lung protection through their contained microRNAs (miRNAs). Previous research has established miR-21a-5p as a key player in pulmonary defense mechanisms. In this study, we utilized a C57BL/6 mouse model of HALI established by hyperoxic conditions (FiO