Background: Coronavirus disease (COVID-19) is a growing concern worldwide. Approximately 5% of COVID-19 cases require intensive care. However, the optimal treatment for respiratory failure in COVID-19 patients is yet to be determined. Case presentation: A 79-year-old man with severe acute respiratory distress syndrome due to COVID-19 was admitted to our intensive care unit. Prone ventilation was effective in treating the patient's hypoxemia. Furthermore, the patient received lung protective ventilation with a tidal volume of 6-8 mg/kg (predicted body weight). However, the patient's respiratory failure did not improve and he died 16 days after admission because of multiple organ failure. Serial chest computed tomography revealed a change from ground-glass opacity to consolidation pattern in both lungs. Conclusions: We report a protracted case of COVID-19 in a critically ill patient in Japan. Although prone ventilation could contribute to treating hypoxemia, its efficacy in preventing mortality from COVID-19 is unknown.