Background. Interleukin 9 (IL-9) has been implicated in the pathogenesis of several tumor types, but the role of anti-IL-9 in pancreatic cancer remains unclear. Objectives. We aimed to explore the mechanism and effects of blockading IL-9 in a pancreatic cancer mouse model. Material and methods. Panc02 cells were injected subcutaneously into mice to establish a mouse model. The mice were randomly categorized into 3 groups-the control group, the immunoglobulin G (IgG) group and the anti-IL-9 group-corresponding to intravenous tail injection of phosphate-buffered saline (PBS), IgG isotype antibody and anti-IL-9 antibody, respectively. Then, the expression of IL-9, interleukin-9 receptor (IL-9r), Janus kinase 1 (Jak1), Jak3, and signal transducer and activator of transcription 3 (Stat3) mRNA was tested with quantitative reverse-transcription polymerase chain reaction (qRT-PCR). Interleukin 9 in the tumor tissue was detected using enzyme-linked immunosorbent assay (ELISA). Western blotting and immunocytochemistry were performed to detect STAT3 and phosphorylation signal transducers and activators of transcription-3 (pSTAT3). Matrix metalloproteinase 2 (MMP2), MMP9 and vascular endothelial growth factor (VEGF) levels were assessed using immunocytochemistry. Results. Tumor weight in the anti-IL-9 group was significantly lower than in the other groups (p < 0.05). There was a remarkable survival benefit in the anti-IL-9 group compared to the other groups (p < 0.05). The concentration of IL-9 in tumor tissue was significantly downregulated in the anti-IL-9-treated mice (p < 0.05). The expression of Jak1 and Jak3 mRNA and pSTAT3, MMP2 and MMP9 proteins in the anti-IL-9 group was lower than that of the PBS or IgG groups (p < 0.05), but the STAT3 and VEGF protein levels showed no significant difference (p < 0.05). Conclusions. Anti-IL-9 antibody could effectively restrain the growth of pancreatic cancer in mice, and this effect may partly occur by blocking the STAT3 pathway.