Sialic acid-binding immunoglobulin-like lectin 15 (Siglec-15) is a member of the Siglec family and functions as an immunosuppressive receptor within the Siglecs superfamily. In recent years, its role in tumor immunity has attracted increasing attention. By modulating the immune microenvironment, Siglec-15 contributes to tumor progression and prognosis,emerging as a novel target for cancer immunotherapy. Immunotherapy for gastrointestinal tumors has become a pivotal treatment approach following surgery, chemotherapy, radiotherapy, and targeted therapy. While PD-1/PD-L1 and CTLA-4 inhibitors have shown efficacy in some patients, challenges such as drug resistance and biomarker identification remain. This review systematically summarizes recent advances in understanding the relationship between Siglec-15 and gastrointestinal tumor immunity, covering its biological characteristics, expression patterns in gastrointestinal cancers, immunomodulatory mechanisms, and potential therapeutic strategies targeting Siglec-15. These findings may provide new insights and approaches for immunotherapy in gastrointestinal malignancies.