This study analyzes the expression and functional role of activating transcription factor 6 (ATF6) in diffuse large B-cell lymphoma (DLBCL) and its effects on disease progression. ATF6, a core component of the unfolded protein response (UPR) pathway, participates in many cellular activities and notably contributes to tumorigenesis. Through a combination of techniques, including immunohistochemistry (IHC) staining to assess ATF6 and pS6K levels, siRNA-mediated ATF6 knockdown, cytotoxicity assays, flow cytometry, quantitative real-time PCR (qRT-PCR), as well as Western blotting, this study clarified the functioning mechanisms of ATF6 in DLBCL and its potential clinical relevance. Further exploration of ATF6's involvement in the mTORC1 pathway was achieved through RNA sequencing (RNA-seq) and gene set enrichment analysis (GSEA). Our findings demonstrate that ATF6 expression is upregulated in DLBCL and linked to poor prognosis, particularly in people aged over 60 with Ann Arbor stage III-IV disease, B symptoms, non-GCB subtype, an international prognostic index (IPI) score greater than 2, and extranodal involvement. Notably, the ATF6 inhibitor ceapinA7 was shown to suppress ATF6 and mTORC1 activation, leading to less cell proliferation and the induction of apoptosis in DLBCL cells. Additionally, ceapinA7 increased the sensitivity of DLBCL cells to adriamycin. The foregoing results underscore the critical role of ATF6 in DLBCL and lay a theoretical and experimental foundation for future targeted therapies and drug development aimed at improving treatment outcomes for DLBCL.