Pulmonary alveolar proteinosis (PAP) is a rare disorder in which lipoproteinaceous materials accumulate in the alveolar compartments. A 72-year-old man was diagnosed with autoimmune PAP with severe respiratory failure. We decided to perform segmental lung lavage (SLL) with fiberoptic bronchoscopy under general anesthesia. If improvement was not significant, whole-lung lavage (WLL) would be done. SLL improved the respiratory failure and computed tomography findings. This case showed improvement in not only the area where lavage was done but also the non-lavaged area. SLL with fiberoptic bronchoscopy under general anesthesia might be an appropriate treatment option for patients with severe PAP.