Osmotic demyelination syndrome (ODS) is an acute demyelinating disorder characterized by the loss of myelin in the center of the basis pons which is defined as central pontine myelinolysis (CPM) and demyelination process in locations outside the pons which is defined as extrapontine myelinolysis (EPM). ODS including CPM and EPM is mainly caused by the rapid correction of hyponatremia. However, there are several reports of ODS in medical condition such as malnutrition, alcoholism, liver transplantation, malignancy, sepsis, electrolyte imbalance including hypernatremia, hypokalemia, hypophosphatemia, and chronic illness. Rarely, ODS was reported in patients with hyperammonemia or hyperbilirubinemia without sodium fluctuations. The symptoms usually correspond to the lesion site and EPM precedes CPM. Because ODS may be irreversible, prevention is more important. Here, we report a case of ODS secondary to the hyperammonemia and hyperbilirubinemia, as it can have unfavorable prognosis.