Abstract: Interleukin-22 (IL-22) is a member of the IL-10 family, which exhibits a similar structure and immune function with IL-10. IL-22 is mainly secreted by Th22, Th1, and Th17 cells, innate lymphoid cells (ILCs), and γδT and NKT cells. IL-22 is mainly involved in autoimmune diseases, malignant tumors, and infective diseases. As such, studies have focused on the function of IL-22 cytokine in the pathogenesis of various malignant tumors. Studies revealing the expression and pathogenesis of IL-22 in malignant tumors possibly provide a new method to treat and prevent malignant tumors. In our study, the discovery, structural characteristics, and functions of IL-22 in malignant tumors are reviewed.