Objective:To the microecological changes and the prevention and therapy by using Bifidobacterium of ulcerative colitis.Methods:Through western rat model.Results:When ulcerative colitis occurs,the weight, Bifidobacterium ,the relative count of the G + bacteria will decrease deeply( P 0 01) companied with the malignant changes of the ulcerative colitis concerned features and the observation under eyes and microscope of the colon.Whereas the contrast and preventional animals have no prominent changes( P 0 05).Conclusion:The rontine method and treatment by using Bifidobacterium both have effects in curing the disease,but treatment by using Bifidobacterium both have effects in curing the disease,but treatment by using Bifidobacterium is better and treatment by adjusting the microecology is a new and better method.