Whereas chemotherapy-induced oral mucositis is a painful and uncomfortable side effect and affects the quality of life and the patient's tolerance for continued treatment, it is important to treat this problem. This study was performed aimed to investigate the effect of L-Carnitine in the treatment of oral mucositis caused by chemotherapy. This study is double-blind randomized clinical trial and will take place on 40 patients over 18 years old and under chemotherapy referring to Imam Khomeini hospital. Blinding was conducted for groups of subjects (patients) participants to measure the outcomes of study (researchers) and data monitoring committee (Recent analysis). Inclusion criteria of the study: bedridden in Oncology unit, consent to participate in the study, without using drugs or any vitamin and mineral carnitine in the past 8 weeks, over 18 years old, Exclusion criteria: the risk of side effects such as nausea or any time the patient refuse to participate in the study. Patients before inclusion are examined of oral health and risk factors of developing oral mucositis. Patients who have inclusion criteria, based on randomized block design in two groups of 20 patients who received the drug or placebo are placed. Patients' demographic information such as age, sex, weight, diagnosis, date of hospitalization, tests, history of other diseases and medication instructions will be registered. In the first group of L-Carnitine at a dose of 3 grams per day and the second group received placebo daily for three weeks since the start of chemotherapy. Of all patients at baseline, before administration of L-Carnitine and then at intervals of one week 10 ml blood samples for biochemical evaluation and testing of the CBC is taken. The use of L-Carnitine and patient adherence to medication side effects, the incidence of mucositis grade rating according to WHO, will be checked every week . During treatment the patient received amount of L-Carnitine also be controlled.