Objective To analyze the dynamic changes to disease activity,colonic inflammation,histopathology,and serum cytokine levels in mice with chronic ulcerative colitis(UC).Methods For UC induction,2.5％dextran sodium sulfate solution was provided ad libitum for 5 days,and to model remission,tap water was supplied for another 5 days in one induction cycle.Disease activity index(DAI),colon length,and pathological changes to colon tissue were determined.The levels of myeloperoxidase(MPO)in colon tissue and of cytokines such as IL-1 β in serum and colon were detected.Results During the three cycles,disease activity was aggravated and colon length shortened in mice during the induction periods,both of which were relieved during the remission periods.The blood appeared was observed in the stool was earlier in cycles 2 and 3.The number of mice with stool blood increased,and their body weight decreased by a small amount briefly,then recovered rapidly.The degree of histopathological damage to the colon and MPO content in cycles 1 and 3 increased in the induction periods and decreased in the remission periods,with the magnitude of change smaller than that of the change in DAI values;and they increased in the remission period of cycle 2.During induction,the spleen index and serum levels of IL-1β,IL-6,and IL-17A increased continuously and were higher than those in the control group at the end of the experiment.Levels of TNF-α were increased in the induction periods and decreased in the remission periods,and the trend in IL-10 change was similar to that of TNF-α.TGF-β content increased and then decreased and was higher than that in the control group at the end of cycle 3.The colon contents of IL-1β,IL-6,and IL-17A showed similar trends of increasing and then decreasing,but there was no significant change in colon TNF-α.The concentration of IL-10 decreased during the induction periods and increased during the remission periods.Conclusions During the induction of chronic UC in mice,the symptoms of hematochezia and systemic inflammatory reactions gradually increased,and the mice showed an increase in tolerance and ability to resist mortality,weight loss,and histopathological injury to the colon.The onset and remission of colonic histopathological damage lags behind symptomatic changes,and there is a gradual shift in colonic inflammation to a pattern dominated by polymorphonuclear neutrophils(PMN)activation.