OBJECTIVE：To observe the efficacy and safety of mesalazine combined with bifidobacterium tetravaccine（live）in the treatment of ulcerative colitis（UC）. METHODS：83 UC patients were tandomly divided into control group（42 cases）and test group （41 cases）. Control group was orally given 1.0 g Mesalazine enteric-coated tablet，4 times a day；test group was additionally given 1.5 g Bifidobacterium tetravaccine tablet（live），3 times a day. The treatment course fr both group was 6 weeks. The clinical efficacy，and serum high sensitivity C-reactive protein（hs-CRP），interleukin（IL）-4，IL-8 levels before and after treatment and the incidence of adverse reactions in 2 groups were observed. RESULTS：After treatment，serum hs-CRP and IL-8 in 2 groups were significantly lower than before，and test group was lower than control group；serum IL-4 level was significantly higher than before，and test group was higher than control group，the differences were statistically significant（P＜0.05 or P＜0.01）. Total effective rate in test group was significantly higher than control group，the difference was statistically significant（P＜0.05）. And there was no significant difference in the incidence of adverse reactions（P＞0.05）. CONCLUSIONS：Mesalazine combined with bifidobacterium tetravaccine（live）is more effective than mesalazine alone UC，with similar safety.