Our purpose is to report a rare case of lipoid pneumonia found in a cat with diabetes mellitus (DM) type II. The cat is an aged, mixed-breed male with a 3-year history of having DM. During the last 16 weeks of its life, the cat presented signs of dyspnea and weakness and was continuously treated by nebulization. Thoracic radiography showed an increased radiopacity of the alveoli. The histopathological findings showed typical lipoid pneumonia, proliferative bronchitis, and diffuse suppurative pneumonia. Chronic pancreatitis with islet amyloidosis and arteriosclerosis was also detected. Immunohistochemistry with anti-Amylin antibody showed a strong positive result in the islet of Langerhans, confirming type II DM in this case. A diagnosis of death from respiratory failure associated with idiopathic lipoid pneumonia was achieved.