A 52-year-old woman with hypertension and moyamoya disease presented with chronic subdural hematoma [CSDH]. The presumed cause of bleeding was ascribed to administrated antiplatelet agents. She responded slowy and clumsily to verbal commands and had right arm weakness. After surgery, her clinical condition improved. But two days after surgery, her symptoms became aggravated and a convulsive seizure was noted within 24 hours. Brain magnetic resonance imaging showed no organic lesion except a small amount of residual CSDH. In addition, there was no laboratory evidence of metabolic brain disease. Moreover, after the administration of an antiepileptic drug [phenytoin], her manifestations disappeared. Therefore, the authors presume that her symptoms were resulted from nonconvulsive status epilepticus [NCSE], despite a lack of ictal period electroencephalographic findings. The authors were unable to find a single case report on postoperative NCSE in Korea. Therefore, the authors report this case of nonconvulsive status epilepticus after drainage of a CSDH in a patient with moyamoya disease.