ObjectiveTo evaluate the efficacy and safety of Qingyusan capsules in the long-term treatment of mild to moderate active ulcerative colitis （UC） with the syndrome of large intestine dampness-heat. MethodA randomized， controlled design was adopted， and 88 patients with mild to moderate UC and syndrome of large intestine dampness-heat were randomized into a Qingyusan （Qingyusan capsules， 0.8 g·d-1） group and a control （mesalazine， 0.4 g·d-1） group， with 44 patients in each group. Three and one patients dropped out in the control and Qingyusan groups， respectively， during the 32 weeks of treatment. The clinical remission rate， mucosal healing rate， and modified Mayo score， TCM symptom score， and short inflammatory bowel disease questionnaire （SIBDQ） score before and after treatment were compared between the two groups. The colonoscopic and pathological changes were observed， and the clinical safety was compared between the two groups. ResultAfter treatment， the clinical remission rate and mucosal healing rate in the Qingyusan group were 72.1% （31/43） and 74.4% （32/43）， respectively， which were higher than those ［26.8% （11/41） and 41.5% （17/41）， respectively］ in the control group （χ2=17.200， χ2=10.843， respectively， both P<0.01）. The treatment in both groups decreased the modified Mayo score， partial Mayo score， and TCM symptom score （P<0.05）， and the decreases in the Qingyusan group were higher than those in the control group （P<0.01）. After treatment， the SIBDQ scores in both groups increased （P<0.05）， and the increase was more pronounced in the Qingyusan group than in the control group （P<0.01）. There was no difference in the incidence of adverse events between the two groups. ConclusionThe clinical efficacy of Qingyusan capsules is remarkable in the long-term treatment of UC with the syndrome of large intestine dampness-heat. Particularly， Qingyusan capsules demonstrates advantages in inducing and maintaining clinical remission， promoting mucosal healing， alleviating TCM symptoms， and enhancing the survival quality of patients， with high safety.