Myxosarcomas are rare malignant neoplasms of soft connective tissues, and there are no reports of hepatic myxosarcomas in cats. An eight-year-old male, neutered, domestic shorthair cat presented with progressive hyporexia, lethargy, and weight loss. An ultrasonography study showed a large abdominal mass connected to the liver. The cat underwent a laparotomy and the mass was removed. Histopathological evaluation of the mass supported the diagnosis of a myxosarcoma. Tumour cells were positive with vimentin and alcian blue stain, and negative with PAS, pan-cytokeratin, s100, epithelial membrane antigen, and α-smooth muscle actin. The Ki-67 index by immunohistochemistry was 6%. The cat was euthanased due to severe lethargy and recumbency. Myxoid soft tissue neoplasms are very rare in cats, and to the best of our knowledge, this is the first report of a hepatic myxosarcoma in a cat. In the present case, the diagnosis was made based on histopathological and immunohistochemical findings and an alcian blue-positive supporting matrix.