Stomatitis is a side effect caused frequently by chemotherapy in patients with esophageal cancer, but a standard treatment for it has not been established. Reactive oxygen species are known to be among the causes of stomatitis induced by chemotherapy or radiotherapy, and some reports suggest that their influences might be reduced by the oral supplementation of glutamine. Elental® is one of the widely-used nutritional supplements, and its pack contains 1, 932 mg of L-glutamine (an especially high amount.). Therefore, we examined the preventive or reducing effects Elental® mey have on oral mucositis. Fifteen patients with esophageal cancer received chemotherapy, six of whom had grade one oral mucositis. All of those six patients entered the investigation, and seven courses of Elental® were administered. After seven courses, all six patients oral mucositis declined from grade 1 to grade 0. This result suggests that Elental® has preventive or reducing effects on oral mucositis.