Objective To establish a mouse model of 5?fluorouracil (5?FU)?induced intestinal mucositis. Methods Different doses of 5?FU were intraperitonealy injected into mice for once or 5 consecutive days. The body weight and diarrhea score of the mice were recorded every day, and peripheral blood and the morphological changes of small intestine were examined at 24 h or 72 h after the last 5?FU administration. Results Compared with the control group, after administered 5?FU, the dosage groups showed various degrees of body weight loss and diarrhea, and the white blood cell and platelet counts in peripheral blood decreased significantly ( P <0.05 or P <0.01). The small intestine showed evident pathological changes after the single dose 400 mg/ kg and the continuous injection of 50 mg/ kg, 100 mg/ kg. The mortality rate was 100% in the 100 mg/ kg group. Conclusions A mouse model of intestinal mucositis can be successfully established by a single injection of 5?FU or for consecutive 5 days, in a dose?dependent manner. The optimal dose for single injection is 400 mg/ kg, and that of the continual injection for 5 consecutive days is 50 mg/ kg.