A 74-year-old man was referred to us for evaluation of a tumor in the right atrium (RA). Transesophageal echocardiography (TEE) showed an unmovable 50x60 mm mass in the RA. Based on histological findings of subcutaneous tumors in the right abdominal wall, he was diagnosed as malignant lymphoma (ML), and treated with a THP-COP regimen. Upon completion of first THO-COP therapy, TEE showed marked regression of the mass and division into 3 masses, one of which showed marked floating movement with a small stalk. To prevent the risk of embolic events, surgical resection was performed. Resected tumors were necrotic tissues. Serial imaging of cardiac tumor and surgical resection is desirable to decrease the possibility of embolic complication.