Mycotic aneurysm are defined as a localized, irreversible dilatation of an artery due to destruction of the vessel wall by infection. Mycotic aneurysm is may potentially progress to rupture and death unless early diagnosis and appropriate treatment. A 69-year old female was admitted with multiple joint swelling and pain. Methicillin susceptible Staphylococcal aureus was isolated from blood and pus. Initial CT angiography demonstrated mild artherosclerotic changes of abdominal aorta and iliac artery. We started intravenous therapy with nafcillin 1.0 gram twice daily, as the antibiogram showed sensitivity for this antibiotic. Initially, leukocytosis subsided, but in the 4 weeks day her conditions (her multiple cellulitis) worsened with persistence fever and other site abscess. The following CT angiography obtained an presentation shows an enlarged abdominal aortic saccular pseudoaneurysm (4cm) in the retroaortic space at celiac axis level. She was died during medical treatment after operation.