A 46-year-old man was admitted to a neighboring hospital because of pneumonia and treated with various antibiotics. However, his respiratory condition worsened after admission, and he was intubated and put on mechanical ventilation. He was transfered to our hospital for intensive examination and treatment. Within several hours, the hypoxemia seriously worsened and the PaO₂/FiO₂ (P/F) ratio was <60. The patient was then treated with extracorporeal membrane oxygenation (ECMO), after which the hypoxemia improved. Rheumatoid factor (RF), anti-CCP antibody and IgG-RF in the serum were elevated. We considered that the cause of his severe respiratory failure was a result of acute lung injury associated with connective tissue disease, such as rheumatoid arthritis. After treatment with steroid pulse and intravenous cyclophosphamide, his respiratory condition was improved. This case suggests that ECMO may be an effective therapy for patients with severe respiratory failure because of acute lung injury associated with connective tissue disease, particularly in cases that have a possibility to respond to immunosuppressive agents.