Summary: Hepatic fibrosis induced by schistosomes is regulated by a complex network of cytokines. T helper type 9 (Th9) cells are a new type of effector T helper cells, which mainly secrete the specific cytokine interleukin‐9 (IL‐9). Interleukin‐9 has been shown to contribute to liver fibrosis in patients with chronic hepatitis B and in a mouse model due to carbon tetrachloride. However, the role of IL‐9 in schistosomiasis fibrosis remains unknown. In this study, we investigated the roles of IL‐9 in schistosomiasis through in vivo and in vitro studies. The in vivo studies found that neutralization of IL‐9 reduced liver granulomatous inflammation and collagen deposition around parasite eggs. The in vitro studies found that the treatment of primary hepatic stellate cells with IL‐9 induced a significant increase of collagen and α‐smooth‐muscle actin. Moreover, we also described the dynamics and relevance of IL‐9 and IL‐4 in mice infected with Schistosoma japonicum. We found that IL‐9 might appear more quickly and at higher levels than IL‐4. Hence, our findings indicated that IL‐9 might play a role in regulating hepatic fibrosis in early‐stage schistosomiasis and become a promising approach for regulating hepatic fibrosis caused by S. japonicum. [ABSTRACT FROM AUTHOR]