The invention provides an application of bacteroides fragilis ZY-312 to prevention and/or treatment of inflammatory bowel diseases (IBDs), including an application of bacteroides fragilis ZY-312 to preparation of medicines, medicine compositions, food, health care products, food additives, and the like for preventing and/or treating IBDs. In vivo and in vitro related experiments confirm that bacteroides fragilis ZY-312 has excellent resistance to the IBD, including ulcerative colitis or the Crohn's disease, does not have toxic or side effect and can be permanently and effectively applied to preparation of the medicines, medicine compositions, food, health care products or food additives for preventing and/or treating IBDs. The medicines, medicine compositions, food, health care products or food additives can be used for preventing and treating IBDs and have important application values.