We encountered a case of consciousness disturbance and respiratory failure due to refeeding syndrome including hypophosphatemia. A 69-year-old female diagnosed as agranulocytosis caused by methotrexate in rheumatoid arthritis, transfered to our hospital for complication with pneumonia, heart failure and disseminated intravascular coagulation. Thereafter she developed acute respiratory failure and consciousness disturbance because of CO₂ retention, she had mechanical ventilatory support. Despite an improvement of CO₂ retention, a somnolence of unknown cause remained for several days. Nutrition support was changed from peripheral intravenous nutrition to total parenteral nutrition (TPN) after admission on our hospital, and serum phosphorus showed a low value. We considered the cause of somnolence as refeeding syndrome especially hypophosphatemia. The serum phosphorus increased with addition of phosphorus to TPN, somnolence and respiratory condition were improved. As a result tracheal tube was able to extubate. It is important to consider the serum phosphorus level carefully in case of start or change of TPN.