Superior mesenteric venous aneurysm (SMVA) is rare and no standard treatment protocol has yet been established. We report our experience in performing surgical treatment for SMVA. A 64-year-old man was found to have a SMVA by computed tomography which had been performed during follow-up for gastrectomy. The SMVA was observed to gradually increase in diameter, and surgical treatment was therefore indicated. We successfully resected the aneurysm and then closed the defect with a bovine pericardial patch. Considering the potential risk of rupture, venous aneurysms that present with a saccular shape and an expanding tendency should be immediately surgically treated.