Background <p>Human umbilical cord mesenchymal stem cell-derived exosomes (hUCMSC-Exos) are a promising treatment for acute lung injury (ALI)/acute respiratory distress syndrome (ARDS), but traditional delivery methods have limitations. Therefore, this study presents a noninvasive therapeutic approach for ALI/ARDS, offering new mechanistic insights and identifying potential therapeutic targets.</p> Results <p>We established a nebulized LPS-induced ALI model that was characterized by diffuse lung injury and high homogeneity. Following inhalation, hUCMSC-Exos were observed to be internalized by pulmonary microvascular endothelial cells. Analysis revealed that hUCMSC-Exos alleviated ALI by reducing the severity of histological damage, pulmonary oedema, lung inflammation and ferroptosis. Additionally, hUCMSC-Exos improved the mitochondrial function of human pulmonary microvascular endothelial cells (HPMECs) via the transfer of mitochondrial components. Subsequent proteomic sequencing of mitochondria isolated from HPMECs receiving different treatments revealed the significant differential expression of ribosomal proteins among the groups. The most significantly upregulated protein, RPS11, was identified as a key mediator; its knockdown blocked the ability of hUCMSC-Exos to suppress ferroptosis and restore mitochondrial function in HPMECs. Mechanistically, hUCMSC-Exos exert their effects by enhancing mitochondria-encoded protein translation.</p> Conclusions <p>We report a mechanism whereby hUCMSC-Exos upregulate RPS11 to promote mitochondria-encoded protein translation, rescuing mitochondrial function, inhibiting ferroptosis in HPMECs, and ultimately alleviating ALI. Validated across multiple models and supported by multi-omics analyses, our findings collectively establish nebulized hUCMSC-Exos as a promising cell-free therapy targeting mitochondrial homeostasis in HPMECs for the treatment of ALI.</p> Graphical Abstract <p></p>