Atrial septal aneurysm (ASA) was reported as a cause of unknown origin of central or peripheral thromboembolism with patent foramen ovale, aortic debris and spontaneous echo contrast. Especially the paradoxical right to left shunt via micro-fenestration on this sac may be the important cause of this embolism. We report a case of 39 year-old female patient who had atrial septal aneurysm with multiple renal infarction. Symptom was improved with aneurysmectomy and patch closure, then long term anticoagulation has been continued.