A case of abdominal aortic aneurysm associated with systemic lupus erythematosus (SLE) is described. SLE is rarely associated with aneurysm of great arteries. Histological investigation revealed marked infiltration of inflammatory cells in the aneurysmal aortic wall. Immunocytochemical analysis using anti-factor VIII-related antigen antibody showed a marked increase of the vasa vasorum with luminal narrowing due to intimal thickning. In this case the major etiology of aortic aneurysm is considered to be non-specific inflammation of the abdominal aorta, not arteriosclerosis.