In the study, a myxoid liposarcoma in the proximal region of the left humerus of a 15-year-old male, shorthair cat was described. Left arm along with scapula was amputated. The cut section of tumor was tan to white with soft multilobulated mass which contained hemorrhagic and necrotic foci as well as mucuous composition. Microscopically, the tumor was composed of round-to-polygonal cells. The cells had numerous round, variable-sized, well-defined, intracytoplasmic vacuoles. The lipid droplets in the cytoplasmic vacuoles of the tumor cells was showed with Oil Red O staining. A myxoid extracellular substance remind of mucin was stained by Alcian blue staining (pH = 2,5). Tumor cells were strongly positive for vimentin, but negative for pancytokeratin and S-100. A polymerase chain reaction (PCR) assay from samples showed no evidence of feline leukemia virus (FeLV) / feline sarcomavirus (FeSV) or feline immunodeficiency virus (FIV) deoksiribonucleic acid (DNA). This case describes a first report of myxoid liposarcoma in a cat.