Carcinomas are the most common malignancies of the esophagus. Primary malignant lymphoma involving the esophagus is rare, with only a few cases of mucosa-associated lymphoid tissue (MALT) lymphoma of the esophagus having been reported. We report the case of a 74-year-old man who was diagnosed with an esophageal MALT lymphoma. Generally, MALT lymphomas are indolent and tend to disseminate slowly; however, the behavior of this disease is not known clearly, and a standard treatment has not been established because of its rarity. Although complete response was confirmed with 36-Gy irradiation, careful follow-up is necessary for the patient.