A 24-year-old woman was admitted complaining of right hemiparesis and episodes of syncope. Computed tomography demonstrated a low density area in the left putaminal region. Intravenous digital subtraction angiography (IVDSA) showed two aneurysms in the distal segment of the right middle cerebral artery. Cerebral emboli from a cardiac source was suspected, and cardioechography was performed. Myxoma was located in the left atrium. The patient was transferred to a cardio surgical unit, and the myxoma was successfully removed. After removal by operation of the cardiac tumor, follow-up third IVDSA was performed. One aneurysm of the distal segment of the right middle cerebral artery had grown larger. On the other hand, the other aneurysm had disappeared. Clipping of the enlarged aneurysm was performed. After the clipping operation of the enlarged aneurysm, a follow-up 4th IVDSA was performed. A new aneurysm of the proximal segment of the left cerebral artery was observed. A follow-up 5th IVDSA was performed, revealing that the new aneurysm was enlarging. No operation was performed, because the aneurysm was the fusiform type. At present, the patient is complaining of slight right hemiparesis and has returned to her job. Here we reported a case of cerebral aneurysm caused by left atrial myxoma.