Inflammatory bowel disease (IBD) is a disease with an immune system malfunction and has a poor prognosis. Several medicines based on the modulation of gut microbes have been proposed. For a study, researchers determined to look at the therapeutic effects of B. adolescentis on IBD, as well as the immunological and microecology mechanisms that B. adolescentis in IBD. In the cohort, the fecal level of B. adolescentis was lower in IBD patients than in healthy adults. Chronic colitis with three cycles of dextran sulfate sodium (DSS) was induced by the researchers to further understand the role of B. adolescentis in IBD. The researchers found the preventive properties of B. adolescentis gavage by dramatically reduced diarrhea score, spleen weight, and increased colon length. As a result, the cumulative histological grading in the B. adolescentis administration group was lower. Also, tight junction protein and the mucin family were also improved after B. adolescentis treatment. Unique impacts were found with reduced pro-inflammatory cytokines like TNF-α, IL-6, IL-1β, IL-18, IL-22, IL-9 as well as enhanced anti-inflammatory cytokines like IL-10, IL-4, and IL-5. Significantly, colon lamina propria in the B. adolescentis had more Treg and Th2 cells, which inhibited severe gut inflammation. In addition to that, 16srRNA sequencing revealed that the B: F ratio in the B. adolescentis group had significantly increased. Specifically, B. adolescentis treatment inhibited the excessive growth of Akkermansia and Escherichia-Shigella in the genus level. In conclusion, B. adolescentis improved DSS-induced chronic colitis by promoting the protective Treg/Th2 response as well as gut microbiota remodeling. Treatment with B. adolescentis on a regular basis may improve the therapeutic effects of inflammatory bowel disease.