OBJECTIVE： To study the effects and mechanism of couplet medicines of Scutellaria baicalensis-Paeonia lactiflora on improving ulcerative colitis （UC） in mice. METHODS： A total of 70 mice were randomly divided into blank group， model group， S. baicalensis group （1.5 g/kg）， P. lactiflora group （1.5 g/kg）， S. baicalensis-P. lactiflora （2 ∶ 1， 1 ∶ 1， 1 ∶ 2， m/m） groups （total amount of 1.5 g/kg）， with 10 mice in each group. Except for blank group， UC model of mice was induced in each group. The next day after modeling， treatment groups were given relevant medicine liquid 0.2 mL/10 g （75 mg/mL， calculated by crude drug mass concentration）， while blank group and model group were given constant volume of normal saline intragastrically， once a day， for consecutive 7 d. After administration， disease activity indexes （DAI） of rats were scored， and the serum levels of TNF-α， IL-1β， IL-6， D-LA and myeloperoxidase （DAO） were determined. The length of the colon was measured and the intestinal mass index was calculated in mice. The activities of medullary peroxide （MPO） and SOD， the levels of NO and MDA were determined in colon tissue. RESULTS： Compared with blank group， DAI score， serum levels of TNF-α， IL-1β， IL-6， D-LA and DAO， the levels of MPO， NO and MDA in colon were increased significantly in model group， while the length of colon， intestinal mass index and SOD level of colon tissue were decreased significantly， with statistical significance （P＜0.05 or P＜0.01）. Compared with model group， DAI score， serum levels of TNF-α， IL-1β and DAO， the level of MDA in colon were decreased significantly in S. baicalensis group （P＜0.05 or P＜0.01）. The serum levels of TNF-α and IL-1β， the level of MDA in colon were decreased significantly in P. lactiflora group （P＜0.05 or P＜0.01）. Above indexes of S. baicalensis-P. lactiflora （2 ∶ 1） group were improved significantly except for the length of colon （P＜0.05 or P＜0.01）. Above indexes of S. baicalensis-P. lactiflora （1 ∶ 1） group were improved significantly except for serum level of IL-6 and the level of SOD in colon （P＜0.05 or P＜0.01）. Above indexes of S. baicalensis-P. lactiflora （1 ∶ 2） group were improved significantly except for serum level of NO （P＜0.05 or P＜0.01）. CONCLUSIONS： The couplet medicines of S. baicalensis-P. lactiflora can reduce the expression of proinflammatory factors， enhancing antioxidant activity of the body and decrease intestinal mucosal permeability so as to improve UC symptom of mice； and the effect of S. baicalensis-P. lactiflora （2 ∶ 1） group is the best.