Abstract: To study the preventive effect of Lactobacillus degrading tryptophan on ulcerative colitis, the content of tryptophan in fermentation broth was determined by high performance liquid chromatography (HPLC). 75 8-week-old C57BL/6N male mice were divided into five groups:Normal group, model group, tryptophan group, 1.0386 group, 1.0386+tryptophan group. PBS, tryptophan, 1.0386 bacterial suspension and the mixture of 1.0386 and tryptophan was continuously administered for 3 weeks. In the last week before the end of the experiment, the mice were given 2.5% dextran sulfate sodium (DSS) for 7 d to induce mice model of ulcerative colitis, and the mice were intragastrically administered. During the modeling period, DAI of mice were recorded.After the experiment, the mice were sacrificed, and colon length, organ weight, and pathological changes of colon tissue were measured. The results showed that compared with the normal group, DSS could significantly reduce the body weight of mice, increase DAI index, shorten colon and cause colon tissue damage, up-regulate proinflammatory factors in serum and down-regulate anti-inflammatory factors (P<0.05). What's more, Lactobacillus plantatus KLDS1.0386 combined with tryptophan could alleviate DSS-induced weight loss, colon shortening, disease activity index and spleen index (P<0.05). In addition, Lactobacillus plantatus KLDS1.0386 combined with tryptophan down-regulate the pro-inflammatory factor IL-6 and up-regulate the anti-inflammatory factor IL-10 (P<0.05). Therefore, Lactobacillus plantans KLDS1.0386 combined with tryptophan could improve the pathological damage of colitis mice.