Background/Aim: Oral mucositis, which occurs frequently in the treatment of cancer, is a major problem. In this study, we aimed to develop a rat model of oral mucositis induced by cancer chemotherapy for quantitative measurement. Materials and Methods: A model animal of oral mucositis was prepared by injecting an acetic acid aqueous solution into the buccal mucosa of rats to which a 5-FU solution had been previously administered. The doses of 5-FU and acetic acid were examined, and a treatment experiment using Kenalog® was performed. Results: The optimal dose of the 5-FU solution and the optimal concentration of the acetic acid aqueous solution were 40 mg/kg and 25%, respectively. Treatment with Kenalog® confirmed that this model mimics immunocompromised oral mucositis. Conclusion: Compared with a mouse model, oral mucositis can be easily observed in this model and provides a large amount of oral mucosal tissue.