A 3-year-old domestic shorthair cat presented with lethargy and anorexia. A blood test showed regenerative anaemia and thrombocytopenia. Thoracic radiographs showed a small amount of pleural effusion. The cat did not respond to treatment and died on the fifth day. Necropsy revealed moderate pericardial effusion, and multifocal coalescing haemorrhages were observed on both atria. Histological analysis revealed that the most severe lesions were located on the heart. Numerous arterioles supplying the heart were partially to completely filled with plump spindle cells that often formed glomerulus-like arrangements within the lumen. Similar vascular proliferative lesions were also found in the liver, pancreas and kidney. Immunohistochemical analysis showed that these intraluminal proliferative spindle cells were positive for anti-von Willebrand factor (vWF). Strongly positive antismooth muscle actin staining was observed at the periphery of these intraluminal proliferations (comprising arteriolar smooth muscle) and certain intraluminal cells (pericytes). The intraluminal thrombi were also positive for vWF. Those thrombi were confirmed as platelet thrombi by phosphotungstic acid haematoxylin and Masson's trichrome staining. These results were consistent with feline systemic reactive angioendotheliomatosis.