Although Mycoplasma pneumonia is frequently observed in immunocompromized patient if, rarely results in acute respiratory distress syndrome (ARDS). The cold agglutinin is positive in 33-76% of patients with M. pneumonia infection. We experienced a case of ARDS due to mycoplasma pneumonia associated with cold agglutinin disease in primary CNS lymphoma. He was a 60-year old primary CNS lymphoma patient with mycoplasma pneumonia and cold agglutinin disease who rapidly progressed to ARDS after 1 cycle of chemotherapy. He completely recovered with roxithromycin, levofloxacin, and ventilator supports. After recovery 2nd cycle of combination chemotherapy and brain radiation therapy was given and, CNS lymphoma is in complete remission until now.