Abstract: As a newly identified T helper cell subset, Th9 plays an important role in anti-tumor immunity. Th9 can be differentiated from CD4⁺ T cells that have been induced by TGF-beta and IL-4. In addition, other CD4⁺ T helper cell subsets can be developed to Th9 cell in particular situations, thereby showing its plasticity. Results of animal experiments have indicated that Th9 inhibits tumor growth and plays a significant role in anti-tumor immunity by secreting related cytokines such as IL-9. A few cytokines and molecules can regulate the differentiation and development of Th9 cells in different signaling pathways. This review will focus on the production, anti-tumor immunity, related mechanism, and signaling pathways of Th9 cells, thereby providing a new field of vision and idea for anti-tumor therapy in the future.