Pulmonary leukemic infiltration is usually asymptomatic, although it may present with critical clinical conditions. It is difficult to diagnose because of its non-specific radiographic patterns and laboratory findings. Therefore, invasive diagnostic procedures are usually required to reach the diagnosis. Leukostasis with leukemic alveoli migration is considered to be its characteristic pathologic finding. Here, we report a case of pulmonary leukemic infiltration requiring mechanical ventilation and extracorporeal membrane oxygenation support that was diagnosed using bronchoalveolar lavage and postmortem sono-guided lung biopsy.