Alveolar epithelial-capillary barrier disruption is a hallmark of Acute Respiratory Distress Syndrome (ARDS). Contribution of mitochondrial dysfunction to the compromised alveolar-capillary barrier in ARDS remains unclear. Mesenchymal stromal cells-derived extracellular vesicles (MSC EVs) are considered as a cell free therapy for ARDS. Mitochondrial transfer was shown to be important for the therapeutic effects of MSCs and MSC EVs. Here we investigated the contribution of mitochondrial dysfunction to the injury of alveolar epithelial and endothelial barriers in ARDS and the ability of MSC EVs to modulate alveolar-capillary barrier integrity through mitochondrial transfer.Primary human small airway epithelial and pulmonary microvascular endothelial cells and human precision cut lung slices (PCLSs) were stimulated with endotoxin or plasma samples from patients with ARDS and treated with MSC EVs, barrier properties and mitochondrial functions were evaluated. LPS-injured mice were treated with MSC EVs and degree of lung injury and mitochondrial respiration of the lung tissue were assessed.Inflammatory stimulation resulted in increased permeability coupled with pronounced mitochondrial dysfunction in both types of primary cells and PCLSs. EVs derived from normal MSCs restored barrier integrity and normal levels of oxidative phosphorylation while EV preparation which did not contain mitochondria was not effective. In vivo, presence of mitochondria was critical for EV ability to reduce lung injury and restore mitochondrial respiration in the lung tissue.In the ARDS environment MSC-EVs improve alveolar-capillary barrier properties through restoration of mitochondrial functions at least partially via mitochondrial transfer.