Endothelial pyroptosis, a pro-inflammatory programmed cell death, promotes endothelial inflammation and is a pivotal process in the initial stage of acute lung injury (ALI). Hydrogen sulfide (H2S), a gasotransmitter primarily dependent on cystathionine γ-lyase (CSE) in the cardiovascular and respiratory systems, plays a protective role during ALI. Nonetheless, the modulatory role and precise molecular mechanism of endothelial endogenous CSE/H2S in the pathogenesis of ALI remain elusive. Herein, we prepared an ALI mouse model using intratracheal administration of LPS (5 mg/kg), and lung injury was assessed by evaluating pulmonary edema, inflammatory response, and endothelial pyroptosis. In this model, H2S production from pulmonary tissues declined in a time-dependent manner, accompanied by a compensatory elevation of CSE protein levels. Treatment with the H2S donor (NaHS) attenuated pulmonary edema, inflammatory cell infiltration, endothelial pyroptosis, and reduced serum levels of tumor necrosis factor-alpha (TNF-α), interleukin-1β (IL-1β), and interleukin-6 (IL-6). Meanwhile, the inducible deletion of CSE in endothelial cells exacerbated these changes. The blocking effect of CSE/H2S on endothelial pyroptosis (evidenced by caspase-11 activation and GSDMD-NT formation) was also confirmed in cultured pulmonary microvascular endothelial cells (PMECs). Mechanistically, H2S-mediated regulation of sirtuin-1 (SIRT1) expression and activation (via sulfhydration) contributed to the modulatory process. Collectively, we uncovered that endothelial endogenous CSE/H2S alleviates endothelial pyroptosis by activating SIRT1, thereby preventing LPS-induced acute lung injury.© 2025 Federation of American Societies for Experimental Biology.