Abstract: Interleukin-21 (IL-21), a member of the IL-2 cytokine family, is predominantly produced by activated CD4+T cells and has a variety of biological effects on lymphocytes and myeloid cells. Since its discovery in 2000, tremendous progress has been made to elucidate IL-21′s induced cellular immune response， especially in the inhibition of hematological malignancies. Preclinical studies have shown that exogenous IL-21 induced the direct apoptosis of B-cell non-Hodgkin lymphoma (NHL) B-cell with expression of IL-21R, making it a potential new strategy for anti-lymphoma therapy. The antitumor effect of IL-21 is mainly mediated through the cytotoxic activity of NK cells and CD4+/ CD8+T cells. This review provides an overview of the biological structure and function of IL-21 and its anti-tumor clinical trials， and illustrates the efficacy of IL-21 in combination with CAR-T cells and monoclonal antibodies.

Key words: IL-21, anti-tumor function, cytokine