Involuntary movement complicated with the postoperative stage of the ruptured cerebral aneurysm is extremely rare. And, the pathophysiology of the involuntary movement has not been established yet. The authors report such a case because of its rarity and to make the mechanism of its appearance clear. The case was a 45-year-old female who was transported to our clinic after the onset of sudden headache. On admission, she had no neurological deficits without severe headache. CT scan revealed subarachnoid hemorrhage, and left carotid angiogram showed an aneurysm at the bifurcation of the left internal carotid artery. On the day of admission, neck clipping for the aneurysm was successfully performed. Postoperative course was uneventful without mild right hemiparesis which diminished until two weeks after operation. Since the 24th day from operation, athetoid involuntary movement occurred to her four toes. 123I-IMP SPECT revealed low perfusion from left frontal base to caudate, and CT scan showed atrophy of the left caudate. Athetoid involuntary movement as postoperative complication of ruptured cerebral aneurysm has not been reported without our case. We suppose it was caused by the ischemic effect of the left caudate due to the operative retraction or the delayed vasospasm after subarachnoid hemorrhage.