BACKGROUND: Subarachnoid hemorrhage (SAH) is a cerebrovascular disease with a very high disability and mortality rate, which brings a huge economic burden to society. It is reported that inhibition of forkhead box O3 (FOXO3) can alleviate brain edema and neuroinflammation after SAH. However, the role and mechanism of FOXO3 in regulating SAH progression need to be further studied. METHODS: Mouse microglia were treated with oxyhemoglobin (OxyHb) to build SAH cell model in vitro. Western blot was used to measure the protein levels of FOXO3, ubiquitin-specific peptidase 30 (USP30), embryonic lethal-abnormal vision like protein 1 (ELAVL1), and pyroptosis-related proteins. Cell proliferation was tested by cell counting kit 8 assay and 5-ethynyl-2' -deoxyuridine assay. Inflammatory factors were detected by ELISA, and cell polarization was evaluated using flow cytometry. Cell pyroptosis was assessed by detecting. Co-immunoprecipitation assay, immunofluorescence colocalization assay, and RNA immunoprecipitation assay were used to evaluate the interaction between FOXO3 and USP30 or ELAVL1. RESULTS: Downregulation of FOXO3 inhibited inflammation, M1 polarization, and pyroptosis in OxyHb-induced microglia. USP30 promoted FOXO3 expression through deubiquitination. USP30 knockdown suppressed inflammation, M1 polarization, and pyroptosis in OxyHb-induced microglia, and these effects were abolished by FOXO3 overexpression. Also, ELAVL1 interacted with FOXO3 to facilitate its mRNA stability. Meanwhile, USP30 increased FOXO3 expression to activate the cyclic GMP-AMP synthase (cGAS)/stimulator of interferon genes (STING) pathway. CONCLUSION: USP30-mediated deubiquitination of FOXO3 contributed to OxyHb-induced microglia inflammation, M1 polarization, and pyroptosis, providing a novel target for the treatment of SAH.