Chemotherapy-induced mucositis, one of the most common complications of chemotherapy, can be subdivided in oral and gastrointestinal mucositis. The patients always suffer from oral pain and ulcers, nausea, vomiting, abdominal pain and diarrhea. 5-Fluorouracil- and irinotecan-based regimens are frequently associated with a higher risk and more severe grade of mucositis. The onset of mucositis is also influenced by the patient’s characteristics including age, sex, genetic polymorphisms, systemic comorbidities. At present, the diagnosis of chemotherapy-induced mucositis is mainly based on medical history, physical examination and gastroenteroscopy, lack of reliable biomarkers for early diagnosis. The principles of diagnosis and treatment mainly refer to the clinical practice guidelines issued. Therefore, this article will review the mechanism, diagnosis, latest preventive and treatment strategies of chemotherapy-induced mucositis for helping clinicians to further correctly understand and deal with the adverse reactions.