Abstract: Abnormal elevation of serum immunoglobulin G4 (IgG4) and abundant infiltration of IgG4-positive plasma cells in diseased tissues are the most common clinicopathological features of IgG4-related disease (IgG4-RD). It can affect almost any tissue and organ, and has a variety of clinical manifestations. Increasing studies have found that as a member of IgG family that negatively regulates immune response, IgG4 is correlated with the occurrence and prognosis of malignant tumors and with tumor immunity. This paper reviewed the relationship between IgG4 and malignant tumors and the role of IgG4 in tumor immunity.