Lymphomatous involvement of the heart is extremely rare at initial diagnosis and presentation of malignant lymphoma. Worldwide, only a few cases have been diagnosed and treated during life and only four cases were diagnosed before death in Korea. We report a case of non-Hodgkin's lymphoma with two right atrial masses detected by chest computed tomography and transesophageal echocardiography. The patient was an 80 year- old man and the presenting symptoms included generalized weakness, weight loss, constipation and low abdominal pain. For diagnosis, the mass of the perinephric area was biopsied under ultrasonographic guidance, and pathologically it was determined to be malignant lymphoma, diffuse large B cell type. The patient was treated with continuous low dose cyclophosphamide and prednisolone vice standard chemotherapy because of advanced age and renal dysfunction. After 2 months of treatment the masses in the atrium and the intraabdominal masses disappeared.