Recently, radiation therapy has been reported to be effective in patients with low-grade lymphoma of mucosa-associated lymphoid tissue (MALT) of the stomach. We describe changes in endoscopic ultrasonographic (EUS) findings after radiation therapy in a patient with low-grade gastric MALT lymphoma. Endoscopic ultrasonography initially showed enlargement of regional lymph nodes and diffuse thickening of the second and third mural layers in the gastric body. Two months after the end of radiation therapy, EUS showed hypoechoic changes in the third layer that corresponded to the ulcer scar but no wall thickening or lymph node enlargement. The hypoechoic changes were thought to reflect inflammatory change. We conclude that EUS is useful for assessing the response to radiation therapy in patients with low-grade gastric MALT lymphoma.