Abstract: Gastrointestinal toxicity are common side effects of chemotherapy, presents as abdominal pain and diarrhea, which seriously affect the treatment and quality of life in patients. Understanding the changes and mechanisms of intestinal flora after chemotherapy will help us fi nd related target to prevent or reduce gastrointestinal side effects. This article reviews the effects of chemotherapy drugs on the structure of intestinal flora, intestinal permeability and their mechanisms.