An 8-month-old male orangutan (Pongo pygmaeus) housed in Everland Zoo-logical Gardens died after having 10 day history of depression, anorexia and acute respiratory distress. On necropsy, the lung failed to collapse and showed diffuse red consolidation. Microscopically, the alveoli were filled with large amounts of red blood cells, fibrin and varing number of hemosiderin-laden macrophages. The alveolar septa were thickened due to infiltrated mononuclear cells and congestion and are occasionally necrotic. Escherichia coli was isolated from the lung, spleen and kidney. The result of antibiotic sensitivity test of the isolated organism was also described.