We reported a clinical case of intra-right atrial giant thrombus adhering to an intravenous hyperalimentation(IVH) catheter. The patient was a 63 years-aged male, and was indwelled the IVH catheter for one month from right subclavian vein to right atrium to improve a malnutrition due to his advanced gastric cancer. Intra-cardiac mass was found in the right atrium by routine transthoracic echocardiography for the preoperative inspection; the giant mass(22 x 20 mm) had a low-echo density with a portion of high-echo density. In transesophageal echocardiography, the portion of high-echo density was found to be an IVH catheter and intra-right atrial mass was pierced by that catheter; however, it was difficult to determine whether the mass was either a vegetation or thrombus. The mass was removed by operation, and was diagnosed as a giant thrombus by histopathological examination. Thrombus should be taken into account as a possible cause of intra-right atrial mass when an IVH catheter was indwelled in the right atrium.