Abstract:IL-17 (interleukin-17) family comprise six members: IL-17A， IL-17B， IL-17C， IL-17D， IL-17E (also called IL-25) and IL-17F. IL-17A is the most characterized member， which induces the expression of antipeptides and cytokines. It plays important roles in host defence against bacteria and fungi， and autoimmune disease pathogenesis. Monoclonal antibody against IL-17A or its receptor proves to be a curative therapy of psoriasis and arthritis. IL-17E promotes allergy responses and the elimination of parasites infection by induction of type 2 immunity-related gene expression. Recently， IL-17C was found to help host prevent from pathogens， and promoted the inflammatory diseases. IL-17 family members are considered to affect certain tumors’ initiation and progression. The signaling pathways and biological functions of IL-17 members other than IL-17A are not yet clear. Thus， deeper research on the functions and mechanism of IL-17 family will provide an important theoretical basis and therapy target for autoimmune diseases， infection， allergy and tumor.