Objective The objective of this study is to investigate the expression levels of Th 9 CD4 + T cells and IL‐9 secretion in peripheral blood mononuclear cells of patients with primary Sjogren's syndrome. Further, this study aimed to investigate the role of Th 9 cells in the occurrence and development of pSS. Methods A total of 20 pSS patients and 20 healthy people, matched with age and gender, were selected as the experimental and control group, respectively. Flow cytometry and ELISA were used to detect the expression of Th 9 cytokines in peripheral blood mononuclear cells and IL‐9 in serum, respectively. These factors were then correlated to other clinical indicators. Results The levels of Th 9 CD4 + T cells and IL‐9 of pSS patients were significantly higher than those of the control group. Th 9 CD4 + T cells and IL‐9 levels in peripheral blood of pSS patients were negatively correlated with salivary flow rate, while IL‐9 level was positively correlated with globulin. The transcription levels of IL‐9 and immune‐related genes including IL‐4, IL‐7, IL‐17, SMAD3, STAT5 and JAK3 were dramatically increased in serum of pSS patients. Conclusion The expression levels of Th 9 in peripheral blood and serum IL‐9 of patients with pSS were significantly increased, which were correlated with clinical immunological indexes. Together, these data suggest that Th 9 cells and IL‐9 may be involved in the pathogenesis of pSS.