Objective:To explore the role of Th9 cells and Bregs cells in immunological pathogenesis of ulcerative colitis(UC)and their correlation with disease activity.Methods:A total of 105 patients with UC who were admitted to Hai'an People's Hos-pital from June 2020 to March 2022 were prospectively included as observation subjects(UC group).Among them,48 cases were in disease remission(remission UC group)and 57 cases were in disease activity(active UC group).According to the severity of the pa-tients'conditions in active UC group,subgroups were divided:mild active group(n=20),moderate active group(n=24)and severe active group(n=13).In addition,50 healthy volunteers during the same period were selected as control group.The proportion of Th9 and Bregs cells in the peripheral blood of patients between the two groups were analyzed by flow cytometry,and the serum levels of IL-9,IL-10,IL-35 and C-reactive protein(CRP)were detected by ELISA.The correlation between Th9 and Bregs cell levels and disease ac-tivity and inflammation degree were also analyzed by Pearson correlation analysis.Results:The proportion of Bregs cells and Th9 cells in patients with UC were significantly higher than those of control group.The CAI score,the proportion of Bregs cells and Th9 in active UC group were higher than those in remission UC group(P<0.05).The ratios of Th9 cells and Bregs cells in patients with severe active UC were significantly higher than those in patients with moderate and mild active UC groups,and the ratios in moderate active group were higher than those in mild active group(P<0.05).The levels of CRP and IL-9 in patients with UC in the active and remission stages were significantly higher than those in control group and higher in active stage than in the remission stage(P<0.05).IL-10 and IL-35 levels in the active and remission stages were significantly lower than those in control group,and the levels in the active stage were lower than those in the remission stage(P<0.05).The levels of CRP and IL-9 in severe active group were higher than those in mild and moderate active groups,and the levels in moderate active group were higher than those in mild active group(P<0.05).The levels of IL-10 and IL-35 in severe active group were significantly lower than those in moderate and mild active groups,and the levels in moderate active group were lower than those in mild active group(P<0.05).Pearson analysis showed that Th9 and Bregs cells were positively correlated with disease activity,CRP and IL-9 levels,and negatively correlated with IL-10 and IL-35 levels(P<0.05).Conclusion:The proportion of Th9 and Bregs cells in peripheral blood of patients with active UC are significantly increased,which are closely related to the occurrence and development of the disease and expected to become good indicators for auxiliary clinical early diagnosis and evaluation of the disease.