Primary superior vena cava lymphoma originating from the endothelium of a large vein is very rare. A 70-year-old man was admitted to the hospital; computed tomography showed a tumor limited to the inside of the superior vena cava, completely occluding the vessel. A transjugular biopsy confirmed the diagnosis of diffuse large B-cell lymphoma, which was diffusely positive for CD30. Rituximab monotherapy followed by five courses of R-CHOP chemotherapy induced a complete remission. There was no recurrence after two years. The pathophysiology of lymphoma derived from large vessels may be different from intravascular large B-cell lymphoma, which usually involves small vessels.