Acute necrotizing encephalopathy (ANEC) is a rare illness with high incidence in East Asia. It is accompanied with respiratory infection, gastrointestinal infections, and high fever with quick impaired consciousness, and convulsion. In this case report, Turkmen 6 month's girl that was introduced after an infection with no disease or clinical abnormalities. She was vaccinated accordingly; initially she had fever with generalized tonic-clonic convulsion (seizures) for 5 to 10 minutes level of consciousness decreased later on. She was transferred to Talghani Medicat Education center in nortern Iran. At the time of admition her vital signs were as below: RR: 30, GCS: 8-9, RP: 110, BP: 90/80. In the patient's history, there was neither Trauma history, nor food or drug poisoning, also no clinical history. After convulsion, the level of consciousness decreased and serum biochemistry showed normal electrolytes concentration. In further follow - up, AST increased to 98 units, ALT to 58 units, and ammonium to 215 units. In CSF Sample, protein level increased to 330 units, without any avidences of pleocytosis, blood, or Serum glucose drop. In CT without contract, hypodensity the cornea in thalamus and caudate cores were seen in 2 sides. The ventricles were normal and there were no signs of bleeding and pressure. In brain M.R.I, abnormal signal in 2 sides, blood samples cultivation, CSF, and testing urine for bacterial infection were negative. The patient was diagnosed with necrotizing encephalopathy and subsequently was treated with metyle prednisolone (20 mg daily). During hospitalization, level of consciousness increased and fever stopped. There was not recurrence of convulsion, but the patients still had some problems in moving, verbal and communication.