Gastrointestinal tumors significantly contribute to cancer-related mortality worldwide. Early detection coupled with effective treatment significantly improves overall survival. Immunoglobulin G (IgG) N-glycosylation, a crucial post-translational modification, undergoes alterations in glycan structures. IgG N-glycosylation is associated with numerous physiological and pathological processes in the human body. Aberrant changes of IgG N-glycosylation play a key role in cancers given the involvement of glycans in cancer progression and immune modulation. These changes affect the binding of the Fc region of IgG to its receptor, in turn, affect the corresponding downstream effects, which are crucial in cancer immuno-surveillance and immune escape. This review aims to explore the latest advancements in understanding IgG N-glycosylation in gastrointestinal cancers, emphasizing its potential as a diagnostic biomarker and therapeutic target. The application of IgG N-glycosylation in clinical oncology could enhance early detection, improve therapeutic efficacy, and enable better monitoring of disease progression and recurrence. Furthermore, we summarized the research progression to provide novel insights into the potential regulatory mechanism of IgG N-glycosylation in gastrointestinal tumors. In all, IgG N-glycosylation holds significant promise for advancing cancer diagnosis and treatment. Further studies are required to fully elucidate its mechanisms and optimize its use in clinical practice.