Background <p>Gliomas are aggressive brain tumors associated with a poor prognosis. Although SIL1, an endoplasmic reticulum chaperone factor, is known to maintain protein homeostasis, its specific role in glioma pathogenesis remains poorly understood. This study aimed to investigate the clinical significance and biological functions of SIL1 in glioma.</p> Methods <p>We performed a pan-cancer multi-omics analysis using TCGA and GTEx datasets to evaluate <i>SIL1</i> expression, its prognostic value, and its associations with genomic instability, tumor stemness, and immune infiltration. Gene set enrichment analysis (GSEA) was utilized to identify potentially involved signaling pathways. For in vitro functional validation, human glioma cell lines (U251 and A172) were subjected to siRNA-mediated knockdown and lentiviral rescue assays to assess cellular proliferation, migration, apoptosis, and epithelial-mesenchymal transition (EMT) dynamics.</p> Results <p><i>SIL1</i> was significantly upregulated in gliomas and correlated with poor patient survival. High <i>SIL1</i> expression was associated with increased tumor heterogeneity (based on MATH scores), DNA methylation-derived stemness indices, and an immunosuppressive microenvironment characterized by the enrichment of M2 macrophages, regulatory T cells (Tregs), and immune checkpoint molecules. In vitro, SIL1 knockdown suppressed glioma cell proliferation and invasion, promoted mitochondrial apoptosis, and mitigated the EMT phenotype, potentially by impairing SNAIL nuclear translocation. Notably, these phenotypic changes were effectively rescued following lentiviral overexpression of SIL1.</p> Conclusion <p>Our findings suggest that SIL1 is a potential prognostic biomarker in glioma. Its elevated expression correlates with increased malignancy, stemness features, EMT, and an immunosuppressive microenvironment, indicating that SIL1 may serve as a promising therapeutic target for glioma intervention.</p>